Classifications

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  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/28—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection
  • H01L23/31—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection characterised by the arrangement or shape
  • H01L23/3107—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection characterised by the arrangement or shape the device being completely enclosed
  • H01L23/3121—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection characterised by the arrangement or shape the device being completely enclosed a substrate forming part of the encapsulation
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  • H01L23/29—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection characterised by the material, e.g. carbon
  • H01L23/293—Organic, e.g. plastic
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  • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L2224/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
  • H01L2224/31—Structure, shape, material or disposition of the layer connectors after the connecting process
  • H01L2224/32—Structure, shape, material or disposition of the layer connectors after the connecting process of an individual layer connector
  • H01L2224/321—Disposition
  • H01L2224/32151—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
  • H01L2224/32221—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
  • H01L2224/32225—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being non-metallic, e.g. insulating substrate with or without metallisation
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  • H01L2224/42—Wire connectors; Manufacturing methods related thereto
  • H01L2224/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
  • H01L2224/45—Structure, shape, material or disposition of the wire connectors prior to the connecting process of an individual wire connector
  • H01L2224/45001—Core members of the connector
  • H01L2224/45099—Material
  • H01L2224/451—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
  • H01L2224/45117—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof the principal constituent melting at a temperature of greater than or equal to 400°C and less than 950°C
  • H01L2224/45124—Aluminium (Al) as principal constituent
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  • H01L2224/42—Wire connectors; Manufacturing methods related thereto
  • H01L2224/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
  • H01L2224/45—Structure, shape, material or disposition of the wire connectors prior to the connecting process of an individual wire connector
  • H01L2224/45001—Core members of the connector
  • H01L2224/45099—Material
  • H01L2224/451—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
  • H01L2224/45138—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof the principal constituent melting at a temperature of greater than or equal to 950°C and less than 1550°C
  • H01L2224/45144—Gold (Au) as principal constituent
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  • H01L2224/42—Wire connectors; Manufacturing methods related thereto
  • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
  • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
  • H01L2224/481—Disposition
  • H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
  • H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
  • H01L2224/48225—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being non-metallic, e.g. insulating substrate with or without metallisation
  • H01L2224/48227—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being non-metallic, e.g. insulating substrate with or without metallisation connecting the wire to a bond pad of the item
• • H—ELECTRICITY
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  • H01L2224/73—Means for bonding being of different types provided for in two or more of groups H01L2224/10, H01L2224/18, H01L2224/26, H01L2224/34, H01L2224/42, H01L2224/50, H01L2224/63, H01L2224/71
  • H01L2224/732—Location after the connecting process
  • H01L2224/73251—Location after the connecting process on different surfaces
  • H01L2224/73265—Layer and wire connectors
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  • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
  • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L24/42—Wire connectors; Manufacturing methods related thereto
  • H01L24/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
  • H01L24/45—Structure, shape, material or disposition of the wire connectors prior to the connecting process of an individual wire connector
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  • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L24/42—Wire connectors; Manufacturing methods related thereto
  • H01L24/47—Structure, shape, material or disposition of the wire connectors after the connecting process
  • H01L24/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
• • H—ELECTRICITY
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  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01019—Potassium [K]
• • H—ELECTRICITY
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  • H01L2924/01077—Iridium [Ir]
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  • H01L2924/01079—Gold [Au]
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  • H01L2924/10—Details of semiconductor or other solid state devices to be connected
  • H01L2924/11—Device type
  • H01L2924/14—Integrated circuits
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  • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
  • H01L2924/151—Die mounting substrate
  • H01L2924/156—Material
  • H01L2924/157—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron [B], silicon [Si], germanium [Ge], arsenic [As], antimony [Sb], tellurium [Te] and polonium [Po], and alloys thereof
  • H01L2924/15738—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron [B], silicon [Si], germanium [Ge], arsenic [As], antimony [Sb], tellurium [Te] and polonium [Po], and alloys thereof the principal constituent melting at a temperature of greater than or equal to 950 C and less than 1550 C
  • H01L2924/15747—Copper [Cu] as principal constituent
• • H—ELECTRICITY
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  • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
  • H01L2924/181—Encapsulation
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  • H01L2924/30—Technical effects
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  • H01L2924/3025—Electromagnetic shielding

Definitions

• This invention relates to electronic devices of the type having electrical components soldered together.
• the invention further relates to such devices in which
• one or more of the components are protected with an environmentally shielding
• the invention thus relates to electronic devices that incorporate one or more integrated circuit chips and carrier assemblies by solder connection of their electrical, leads to contacts connected or connectable to other circuitry in the device.
• the invention relates to manufacture of such devices using heated, flowing solder to bond the electrical leads to
• circuits and supports therefor, including those supports commonly referred to as circuit
• IC IC bonded to a carrier as the support.
• the IC has incoming and outgoing (I/O) electrically conductive leads to electrically connect itself to the carrier as an I/C/carrier assembly.
• I/O incoming and outgoing
• the IC can be bonded to a carrier (or lead frame) having mating incoming and outgoing electrically conductive leads.
• the carrier is typically composed of FR4 epoxy boards, bis-maleimide circuit boards, copper lead frames, Kovar lead frames, flexible circuitry
• the carrier will contain electrically conductive laminar leads typically having fine pitch.
• the material bonding the IC to the carrier can be organic such as any suitable thermosetting or
• thermoplastic polymer some containing thermally conductive or electrically conductive fillers, or the bonding material can be inorganic and composed of a solder, solder paste,
• the IC After assembly of the IC and carrier, the IC is electrically connected to the carrier
• the IC and carrier assembly is protected from the environment by encapsulation with a suitable encapsulant for eventual use in an electronic device.
• the encapsulated assembly leads are juxtaposed with device contacts connected
• thermodynamic polymer portions over thermostatic polymer portions so as to endure soldering temperature cycles without degradation. It is a still further object to provide to the IC assembly with a
• thermal wells function by incorporating the heat flux by randomizing
• a further object is to attach the entire encapsulated IC/carrier assembly to main circuitry to be soldered, e.g. by being passed over wave solder to create the solder contacts with the main circuitry while maintaining
• thermodynamic polymer chain amorphous polymer chain portions, the proportion of the thermodynamic polymer chain
• the invention further provides the product of the foregoing method and more generally an electronic device comprising a carrier having a contact and an integrated circuit chip
• the chip having a lead electrically connected in hot-
• the chip having a protective composition congruent therewith and adhering thereto, the composition comprising a resin having thermostatic crystalline polymer chain portions and thermodynamic amorphous polymer chain
• thermodynamic amorphous polymer chain portions being present in such
• thermostatic polymer chain portions remain congruent and adherent to the chip in their locus of original application after solder heat contact.
• oligomer comprising a generally straight-chain polymeric moiety having a molecular weight between about 100 and 20,000 daltons and substituted on about every second to fifteenth in-chain carbon atom and effective to produce three-dimensional twisting and winding atactically, syndiotactically or
• the method further includes selecting
• the first reactive component prepolymer aliphatic diisocyanate from methylene dicyclohexane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate, the prepolymer being comprised of from 3 to 50% by weight of the diisocyanate,
• an aliphatic diamine selecting as the aliphatic diamine a primary or secondary aliphatic diamine comprising a diamino alkane, or an alkyl, alkoyl, aryl, aroyl, or alicyclic-subsfituted diamino alkane, or specifically selecting the aliphatic diamine
• diamine from ethylene diamine, piperazine, n-aminoethyl piperazine, diethylene
• the method further contemplates using with or in place of the aliphatic diamine an aromatic diamine, such as a primary or secondary aromatic amine having di- or multifunctionality and a molecular weight of less than about 2000 daltons, e.g. 3,5-
• diethyl-2,4-toluene diamine di-(3, 5 -methyl thio)-2,4-toluene diamine, methylene-bis- orthochloro aniline, methylenedianiline, methylene-bis-methyl anthranilate, m-phenyl diamine, trimethylene glycol-di-p-amino benzoic ester, or amine capped polyols.
• the method typically employs a the oligomer polymerized linear, cyclic or
• alkanes and alkenes branched alkanes and alkenes, and alkanes or alkenes polymerized with alkenes or alkanes respectively or alkynes, e.g. homo-and co-polymers of ethylene, propylene, butylene, vinyl, allyl, chlorinated vinyl, diene monomers, oligomers and polymers,
• polyvinyl chloride including polyvinyl chloride, ethylene polymers, propylene polymers, dienes, ethylene- propylene polymers, polyisoprenes, natural rubbers, polybutylene polymers,
• butadiene as the oligomer, the polymers having a molecular weight of less than about 4000 daltons.
• the invention electronic device typically employs as the resin the polymerization
• oligomer formed of an aliphatic or aromatic diamine and an oligomer, the oligomer comprising a generally straight-chain polymeric moiety having a molecular weight between about 100 and 20,000 daltons and substituted on about every second to fifteenth in-chain
• prepolymer aliphatic diisocyanate comprises methylene dicyclohexane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate, the prepolymer being comprised of from 3 to 50% by weight of the diisocyanate, the prepolymer being reacted with methylene dicyclohexane diisocyanate, isophorone diisocyanate, or hexamethylene diisocyanate present in an amount from 5 to 15% by weight of the first reactive component;
• the amine comprises a primary or secondary aliphatic or aromatic diamine;
• the oligomer comprises polymerized linear, cyclic or branched alkanes and
• alkenes, and alkanes or alkenes polymerized with alkenes or alkanes respectively or alkynes e.g. homo-and co-polymers of ethylene, propylene, butylene, vinyl, allyl, chlorinated vinyl, or diene monomers, oligomers and polymers, such as polyvinyl
• polystyrenebutadiene polymers polystyrene-butadiene polymers
• halogenated polymers and preferably polymers of 1,3 -butadiene as the oligomer, the
• polymers having a molecular weight of less than about 4000 daltons.
• thermodynamic polymer portions to so respond and sufficient thermostatic polymer portions to maintain the physical strength and adherence of the encapsulant on the substrate), and Secondly, a resistance to scission of the polymer chemical bonds under the temperature conditions and for the period of a soldering cycle.
• a two part polymer precursor composition was prepared as follows:
• Step l 28.00 grams of methylenedicyclohexane-4,4'-diisocyanate were placed into a
• Step 1 pre-polymer reaction was completed and the prepolymer cooled
• Step l 83.00 grams of 2800 MW, di-functional, hydroxyl-terminated polybutadiene resin (R45HT, Elf Atochem, North America) were weighed into a cup, followed by 15.0 grams of diethyltoluene diamine (Ethacure 100, Ethyl Corporation), 1.00 grams of
• the foregoing reagents will provide the resulting urethane polymer with sufficient amorphous/rubbery phase portions in the overall composition based on the equation of thermoelasticity.
• the composition reagents have differential reactivity
• thermodynamic portions This is in excess of the 74 percent predominance of thermodynamic portions
• Parts A and B were dispensed pneumatically side-by-side through a static mixer
• FR4 and Alumina samples were first prepared by heating the
• the alumina and FR4 samples passed the Solder Reflow Test with no visible signs of degradation or delamination.
• the example material deposited globs thus will successfully withstand the highest level (level 1) of JEDEC Test Method, A112 for large 28 mm x 53 mm
• the example polymer also meets the two criteria of lack of degradation under
• thermodynamic versus thermostatic portions in the resin the example resin contains approximately 74% amorphous and thermodynamic
• thermodynamic portions which shift without weakening the resin or causing the nondynamic or thermostatic crystalline portions to expand, or shift, or to lose their
• thermodynamic portions can this result be obtained. While that specific proportion will vary with the resins involved, the example resin has approximately 80%>
• thermodynamic portions and thus about 20%> thermostatic portions.
• thermodynamic portions sometimes called thermal
• resin portions to provide sufficient thermal wells to enable sufficient internal relief of stresses when utilized as an encapsulant, and from its crystalline or thermostatic portions and its chemical constitution sufficient resistance to bond breaking for a period
• thermodynamic phase or portions in the foregoing resin can be calculated taking into account densities, coefficients of expansion, elastic modulus and heat capacities of pure crystalline and amorphous phases by the urethanes as set forth in detail below. These values can be approximated as follows:
• ⁇ c 50 ppm/°C for the crystalline phase
• the amorphous rubbery segment must be a minimum of 74%> to relieve all internal stresses within the encapsulant during the excursion.
• the volume fraction of the rubbery amorphous phase must be at least
• Integrated circuits have historically been encapsulated with various materials in order to provide mechanical protection and a hermetic seal.
• the reasons for mechanical protection are obvious.
• the reason for providing a hermetic seal is to reduce or
• integrated circuit assembly 10 comprises a semiconductor device component 12 bonded to a substrate 14 with adhesive 16.
• the device component 12 has leads 18, 22 electrically connected to contact pads 24, 26, respectively.
• the assembly 10 is
• the assembly 10 has an array 32 of electrical conductors thereon which are registered with a like array 34 on the carrier 36 and soldered together by wave solder or other means, the assembly being attached to the carrier by legs 38,
• a sufficiently heat resistant encapsulating resin 28 may nonetheless be problematical if it expands in a manner that destroys the leads 18, 22 or their connection, or distorts the assembly 10, as hereinafter explained.
• the encapsulant and the component for the rigors of automated soldering systems such as wave soldering be an important consideration in selection of materials.
• the encapsulant resin part of the IC/carrier assembly the cured encapsulant structure as adhered to the IC/carrier should not degrade, become thermoplastic or revert to its constituents upon exposure to soldering processes. Further, the encapsulant resin should not harbor substantial amounts of moisture or other solvents which will boil, outgas or
• encapsulant will have a structure which will match, as closely as possible, the CLE of
• the substrate thus to minimize the strain between the IC, substrate or imbedded wires on the one hand and the encapsulant on the other.
• Epoxies and acrylate encapsulants are typically modified in order to achieve a
• substrate can have CLEs ranging from to 2 ppm/°C to 20 ppm/°C.
• CLEs ranging from to 2 ppm/°C to 20 ppm/°C.
• unfilled epoxies and acrylates have CLEs ranging from 80 ppm/°C to 150 ppm/°C.
• Silicone rubbers have even a considerably higher natural CLE. Therefore, these epoxy or acrylate compositions typically need to be modified by the admixing of low CLE (2
• composition to the IC/substrate assembly For modified epoxies and acrylates, the
• mismatch of the CLE or the strain can be minimized to within a few ppm/°C. Yet the
• differential stresses between the IC/encapsulant, or substrate/encapsulant and wires/encapsulant can be very large. This is because the moduli of the modified epoxy and acrylate resins are themselves typically very large. The differential stresses between the IC, substrate, or wires and encapsulant are nearly approximated by the product of
• the present invention selects an elastomeric material
• Silicone rubber is the major elastomeric material to have been considered as an
• Silicone rubber has the ability to relieve localized stresses in the high
• Silicone rubbers are, however, problematic in that silicones are sufficiently polar that
• Additional criteria for an electronic device encapsulant include processability.
• the encapsulant must be a flowable liquid to properly coat the IC/substrate/wire
• a small amount of encapsulant is dispensed either in a single glob, or by
• the pattern can be generated by adjusting the dispensed amount for each dot or stream with a programmed dispense rate timed to the shift of a multi-axis table
• a major aspect of providing a quality encapsulation of the IC has to do with the flow properties of encapsulant. Three conditions are required of the flow:
• the flow of the dispensate must be sufficiently controllable in order to generate a square or rectangular shape approximating the dimensions of the IC; 2.
• the dispensate must have sufficient flow so the glob, stream or dots meld together without entrapment or striations; and,
• the flow of the dispensate must be sufficiently leveling so that the encapsulated pattern has a level surface (i.e., has a minimum radius to its crown). Once the encapsulant is dispensed over the IC assembly, it must be cured.
• encapsulant can be immediate cured or it can be immediately gelled to prevent
• Cure can be by a
• thermosetting process involving a one-part resin containing a latent hardener which is thermally cured or light-cured, or a two-part resin/hardener system which is chemically
• any break in the hermetic seal can create a reduced product life. So it is advisable that any selected encapsulant be tested using preconditioning to humidity and then be subjected the conditions of soldering.
• IPC SM 786A paragraph 4.152, establishes various levels of preconditioning and test standards for evaluating encapsulated IC structures. Level 1, the most severe, represents
• the invention provides an electronic device having an IC assembly encapsulated with an elastomer meeting all of the criteria, specifically a
• thermodynamic portions i.e. the amorphous portions
• the encapsulant and substrates the latter provides necessary strength, and the whole resist failure from soldering heat exposure and maintains its integrity during the above-
• the invention approach involves the determination of the ideal elastomer
• An ideal elastomer is herein defined as an elastomer which has
• the entropic thermal wells are related to the internal structure of the encapsulant which is imparted with as much entropic character is possible, taking into consideration that the mass needs to maintain some minimum mechanical protection by incorporating or dispersing a certain minimum level of crystalline and/or glass phases within the morphology.
• Crystalline or glassy structures obey the Hookian principles of expansion when incorporating a heat flux based on that heat energy taking those atoms out of their rather
• Thermal wells relate to heat capacities. Two types of thermal wells can be delineated: Enthalpic thermal wells and entropic thermal wells. Enthalpic thermal wells will allow a rise in temperature but protect the bonds, in which these wells reside, from
• Entropic thermal wells can absorb heat through randomizing processes.
• Enthalpic thermal wells are those provided by conjugated structure. Conjugated
• Rubbery polymers are characterized by entropic and not enthalpic factors.
• a rubbery polymer may be considered as starting at state (S 0 ) where it is at room temperature and no stresses are on the encapsulant. The encapsulant is heated to a semi-
• the polymer continues to be heated as it makes a transition from semi-heated
• thermodynamic basis in this description enables it to be shown mathematically what happens when in the manufacture of electronic devices there is utilized an encapsulant which is a rubbery polymer having essentially all entropic character, particularly where the elastomeric encapsulant is partially constrained by the substrate to which it is bonded and the IC which it encapsulates. Further, what is
• the capacity to relieve stress has to do with designing the encapsulant with an entropic thermal well.
• This cylinder contains strictly crystalline or glassy materials obeying or nearly obeying Hookian elastic principles.
• This cylinder contains strictly amorphous materials
• V! Vo + ⁇ V.
• the encapsulant is attached to some IC assembly including a chip and substrate
• encapsulant are minimized and inconsequential at the reference temperature of 25 °C.
• F/A is another expression for stress which can be otherwise measured under
• ⁇ c is the differential linear coefficient of expansion between the substrate/IC
• thermoelasticity equation tells one that the conformance in the x axis allows for conformance on any yz plane contacting
• This heat can be expressed as a function of the force of conformance (a force of forgiveness) times a change in length:
• This force of forgiveness can be expressed as the differential force with respect to a temperature change times that differential temperature change:
• dE ' p • A • (Cp-Cv)/T)(dT/(dL) P , adiabatic dT • dL
• That attachment is the IC/substrate assembly.
• the encapsulant mass must have some minimum volume of
• thermodynamic morphology ⁇ V mixed with crystalline morphology Vo to make up the
• thermodynamic energy for the volume Vj is expressed as :
• volumetric change as any length change (Lj - Lo) for any volume Vo and original length
• thermal well mass ⁇ V can decrease.
• dip temperatures can have an sufficient amorphous content yet still not meet the conditions of an ideal encapsulant. That is, it is fundamental that the elastomer must have bonds whose bond energies are sufficiently high so that destruction of the bonds does not occur, despite the presence of a thermal well.
• the thermal well allows internal energy to be re-distributed to minimize internal
• thermodynamic domains as set forth herein are required for the results shown in the invention electronic devices.
• the raw material ingredients were selected for their lack of ionic contaminants.
• silica (Malvern Chemical) were blended. The materials were mixed and heated to 200
• Part A was packaged in one side of a 50cc dual cartridge. Part B
• silica (Malvern Chemical) were blended. The materials were mixed and heated to 200
• Parts A and B were dispensed pneumatically side-by-side through a static mixer
• This composition is essentially entirely crystalline/glassy and thermostatic.
• Example 1 Tests in the manner of Example 1 showed that these globs, without humidity preconditioning, were capable of withstanding solder bath conditions for in excess of 15 seconds and for up to 2 minutes when not attached to rigid printed circuit board substrates. These same samples, however, indicate poor performance in terms of
• composition was theoretically required to have 182 percent amorphous phase based on the thermodynamic parameters and the above equation of
• thermoelasticity It had zero percent and was 100 percent crystalline — far from the
• thermoelastic equation above correctly predicts the behavior.
• the encapsulants have the ability to stress-relieve internally.
• thermodynamic composition or thermal wells to resist warping and delamination during a solder dip. From the application of the general equation above, it is seen that the thermodynamic composition had to be in excess of 100 percent- an unreasonableity, as will now be shown. The composition has essentially 100 percent crystalline or glassy phase.
• amo ⁇ hous rubbery phases ⁇ V must be a minimum of 182 %> of the total volume or
• An encapsulant body can be envisioned which has heat flowing into it (where the heat flow related Fourier's Law with the change in heat flow across a laminae (x,))
• the strain is related to a stress through the thermal coefficient of
• an effective encapsulant resin will have the largest thermal well possible ⁇
• the elastomeric encapsulant will have randomly dispersed relaxed polymer
• the encapsulant can stretch, compress or conform because we have selected an elastomer. So, what is gained by utilizing an elastomer? The localized straining (stretching, compression or re-
• the non-contact (air-cure) surfaces have the particular freedom to do so. So as localized strains occur at the corners of the IC, the relaxed portions of the
• encapsulant can acquire some strain to relieve the excessive strains in the localized
• thermoplasticity maximizes the difference between the entropy of the
• the overall goal is to provide enough enthalpic and entropic
• interfaces relate to the product of the differential strain ⁇ L times the modulus of the
• matched-CLE resinous, high-modulus polymer such as an epoxy or acrylate which are crystalline or glassy and have characteristics which are Hookian.
• rubbery elastomer can stress-relieve in these localized areas by virtue of averaging the
• the large volume of non-contact surfaces are free to stress-relieve the more
• the polymer be sufficiently elastomeric
• hysteresis relates to the amount of stored heat within the constrained elastomer as it is temperature-cycled in a
• the rubber will be in its most random state when it is relaxed - not having external forces applied to it.
• the rubbery character of the polymer is experienced when an external force is applied to the rubber, either by stretching it or by
• the end-to-end distances of the polymer will increase as the polymer is being rapid heated and stressed to reach state (SO.
• SO stressed to reach state
• the restoring force relates entirely to the probability that the chains will reside in a number of random states upon release of the external force.
• this anomalous behavior of a rubbery polymer is to consider the average end-to-end distance within a relaxed polymer chain. If the average end-to-end chain distances of all the possible random configurations of the relaxed state is small, then the average extension of the random end-to-end distances to the limiting pleated chain structure will be considered.
• a large magnitude of average polymer chain end-to-end extension relates to macroscopic extensibility of the rubbery polymer and to the magnitude of the thermal well. This concept is simplistic but goes a long way to describing the nature of a
• the extensibility of the polymer has to do with the difference between the end-
• the drunk may have taken a long walk where the overall distance is
• random walk pertains to random structure
• random structure pertains to a mono- dimensional polymer in its relaxed state. If one considers the most ordered structure for a general type of polymer structure, it will be a pleated straight-line path (except for the most trivial case). In the trivial case, an sp carbon-carbon (or other atomic structure of the chain) will be
• the end-to-end distance is the average distance between the two ends of a polymer chain. This end-to-end distance is determined by the summation of the in-chain
• each type of polymer has in-chain bonds which are encouraged to twist to one degree or another. For example, carbon-carbon bonds which contain few or no
• this structure can have conformations in three dimensions, but the probability that
• a poly-oxy-propylene oxide polyether has substituents which require every third carbon-
• the poly-oxy-ethylene oxide polyether soft segments in the random state will have a longer average end-to-end distances than a poly-oxy-propylene oxide polyether structures because the latter is taking a more three- dimensional walk.
• the conformational twists can be isotactic, syndiotactic or atactic.
• the chain can be twisted right-handedly or left-handedly, twisted into some alternating pattern or it can have random twisting. In all of these cases, the combined twisting will result in shorter end-to-end chain distances than if there were no twisting at all.
• Polymers which have sp carbon-carbon, sp2 carbon-carbon or sp3 carbon-
• carbon bonds (or in-chain non-carbon atoms) can be visualized as taking random walks.
• polyether polyether
• polyurethanes composes of poly-oxy-propylene units have one methyl substituent per each 3-atom-in-chain propylene unit leads to twisted conformational structure.
• Polyether polyurethanes have considerable rubbery character.
• the lowest modulus material (the encapsulant) starts to strain as internal stresses occur at the surfaces of the IC, wires and substrate.
• the polymer chains become more ordered and the some of the initial random
• the ability of the structure to make conformational changes relates to the energy
• the rubber band has long chains which are essentially three-dimensional and extend in all directions in random
• the poly-cis-isoprene of natural rubber contains some in-chain methylene groups which have pendant methyl groups. These methyl groups, along with some in-chain unsaturation, provide slight barriers to rotation.
• the invention meets the practical
• Polyurethane structure is mo ⁇ hologically distinct from other polymers
• urethane linkages provide regular structure and strong hydrogen bonding, so tight
• Amo ⁇ hous phases can be created by selecting the optimum
• amo ⁇ hous oligomers and reacting these with isocyanate which had been knitted to the glassy phases.
• the random and ordered portions of the polymer will exist within the amo ⁇ hous phases of the polyurethane. So maximum extensibility of the polyurethane will need to be achieved by selecting the most advantageous amo ⁇ hous oligomers.
• Diffuse structure produces the domains of glassy and amo ⁇ hous phases which have the minimum volume of phase-segregated material per mixed boundary material. In order to maximize the thermal well capability of the amo ⁇ hous
• amo ⁇ hous oligomer fluid matrix is designed so the developing glassy domains are only
• the major polyurethane formula reactants (the isocyanate prepolymer, chain extenders and amo ⁇ hous oligomers) have the peculiar ability to start out as rather
• the isocyanate itself is non-polar. If the isocyanate has parent aliphatic or aromatic structure, the overall character of the isocyanate is non-polar. The isocyanate can have some induced polarity. So it can be considered to be intermediate between having polar and non-polar character.
• the oligomeric groups and chain extenders can range from having polar character to non-polar character.
• urethane or urea phases to be formed are substantially more polar than the parent matrix
• glassy-forming chain extenders which are have a substantially more polar character than the amo ⁇ hous
• glassy domains will be on the brink of being insoluble or immiscible, but allowing
• amo ⁇ hous oligomers the isocyanate/chain extender glassy segments have a chance to form rather large and mature domains within the amo ⁇ hous oligomer-matrix fluid. Then the amo ⁇ hous oligomers react and knit the glass domains together to form highly differentiated glassy and amo ⁇ hous mo ⁇ hology.
• the two classes of isocyanates, aromatic isocyanates and aliphatic isocyanates have substantially different
• Aromatic isocyanates react substantially faster than aliphatic isocyanates. In general, there are three classes of active-hydrogen groups effective for reaction with
• isocyanates for encapsulant materials 1) aliphatic amines; 2) aromatic amines; 3) aliphatic oligomers bearing primary and secondary hydroxyls.
• Aromatic isocyanates with Aliphatic amines 1.
• aliphatic isocyanates/aliphatic hydroxyls is very distinct, and phase segregation can be
• amo ⁇ hous polymer chains can be knit to the glassy domains.
• the length of the amo ⁇ hous polymer plays a significant role in achieving
• amo ⁇ hous oligomer chains needs to be at least 300 daltons; and it is better that
• the length be at least 1000 daltons between cross-links or between the glassy domains.
• Aromatic isocyanates, aromatic amines and polybutadiene structures furnish conjugated double-bonded structure capable of providing enthalpic thermal wells. Producing Minimal Internal Stressing in Polyurethanes
• Polyurethanes can be designed for creating minimal stressing at the various interfaces with the IC/assembly by minimizing the modulus of the entire mo ⁇ hological structure and, in particular, the amo ⁇ hous segments. Selecting a combination of aliphatic isocyanates with aliphatic hydroxyls produces low modulus amo ⁇ hous
• Dissipating localized stresses in polyurethanes is accomplished by ensuring that the various amo ⁇ hous segments are sufficiently integrated through the glassy domains.
• the glassy domains must themselves have the ability to re-align and conform
• thermodynamic reversibility of the polyurethane can be maximized and
• Polybutadiene oligomeric segments have vinyl substituents, the vinyl substituents
• the vinyl group is
• the urethane polymer chains need to have sufficiently strong bonds of chain extension and cross-linking to withstand bond breaking, degradation and reversion during soldering. Accordingly one wants to form the maximum number of strong
• poly-oxy-propylene oxide ether oligomers poly-oxy-ethylene oxide ether polyols (Carbowaxes), polytetramefhylene oxide ether polyols, or polyols of polyester such as
• bond energies (ability to withstand bond-breaking) involved.
• ether bonds require less energy to break as do C-N bonds which require only 66 Kcal/mole.
• the most heat-stable urethane elastomers to solder processes are those which avoid C-O-C ether bonds.
• the preferred polymers are polyureas or polyurea/polyurethanes combinations which we nominally refer to as polyurethanes.
• polyurethanes another practical consideration is that the reactivity
• An aromatic amine provides an enthalpic thermal well associated with resonance of the aromatic group.
• urethane linkages If a urethane linkage needs to be formed (such as for
• isocyanate help stabilize the carbonyl group of the urethane linkage.
• aromatic substituent on aromatic isocyanates destabilizes urethanes because of the unbalanced electron withdrawing effects on the carbonyl of urethane linkage.
• linkages do not suffer from the electronic imbalance as do polyurethane linkages. So, even though the two adjacent aromatic groups create electronic deactivation to the urea linkage, they do so in an electronically balance manner avoiding the strong dislocation
• the aliphatic isocyanate prepolymer component is preferably selected from
• diisocyanate and is present in the amount of 3% to 50%, preferably in the amount of
• the aromatic isocyanates from which the Step 2 additions are made are preferably selected from diphenylmethane diisocyanate, toluene diisocyanate, and naphthalene diisocyanate and are present in the amount of 1% to 25%>.
• Aliphatic amine chain extenders an be used for the pu ⁇ ose of seeding the formation of glassy segment domains. If this is to be the pu ⁇ ose, they can also be used to create a chemical thixotrope for damming pu ⁇ oses. Aliphatic amine chain extenders
• amines are preferably selected from primary or secondary amines, having di-functionality or multi-functionality, preferably having a molecular weight of 2000 daltons or less, more preferable 500 daltons or less. Further the amine is preferably a diamino alkane or an
• alkyl alkoyl, aryl, aroyl, or alicyclic substituted diamino alkane, i.e., ethylene diamine,
• piperazine n-aminoethyl piperazine, diethylene triamine, triethylene tetramine, higher members of this homologous series, including piperazine cyclics, l,3-bis(aminoethyl)
• cyclohexane 1,4 diaminocyclohexane, m-xylene diamine.
• This group includes amines from the amino-capping of low molecular weight polyols such as Jeffamine D230,
• the Part B component present in low levels, preferably at levels lower than 10% by weight of the Part B component, and ideally at a weight of less then 3% by weight of the Part B component.
• Aliphatic amine chain extenders are used for the pu ⁇ ose of seeding the
• aromatic amines are preferably selected as chain extenders. This includes a
• aromatic amines having di-functionality or multi- functionality, preferably having a molecular weight of 2000 daltons or less, more preferable 500 daltons or less.
• aromatic amine is preferably 3,5-diethyl-2,4-
• methylenedianiline Amicure 101, methylene-bis-methyl anthranilate, m-phenylene diamine, trimethylene glycol-di-p-amino benzoic ester (Polacure, Air Products), aromatic amine capped polyols such as Polamine 650, Polamine 1000 and Polamine
• Amo ⁇ hous Oligomers are necessary for creating the prepolymer, quasi- prepolymer and for imparting amo ⁇ hous segments to the polymer through the Part B
• amo ⁇ hous segments are preferably selected from functional
• the functional groups composed of a group of active-hydrogen-bearing functions, including hydroxyl groups, primary and secondary
• amo ⁇ hous segments are preferably selected from essentially straight chain structures which have the maximum ability to reconform without creating chain entanglement from chain branching. However, some slight
• branching is encouraged to provide for overall cross-linking integrity of the polymer.
• amo ⁇ hous segments are preferably selected from functional polymers
• the hydrocarbons can be composes of linear, cyclic or branched alkanes, alkenes and alkanes and alkanes, and alkanes, alkenes mixed with alkynes.
• the chains will contain in-chain carbons having, on
• Alkenes can be non-conjugated or conjugated, being either cis- or trans-, preferably having substituents which are alkyl, vinyl, halogenated alkyl or vinyl, capable of being other substituents such as acetate, acrylate, nitrile, amide, etc.
• substituents can be derived from homopoiymerization or co-polymerization with and amongst ethylene, propylene, butylene, vinyl, allyl, chlorinated vinyl, diene monomers, oligomers and polymers.
• These homopolymers and co-polymers can include combinations such as polyvinyl
• polymers polyisoprenes including natural rubbers, polybutylene polymers, styrenebutadiene polymers, halogenated polymers such as Viton, Hypalon and latices
• amo ⁇ hous segments are more preferably selected from
• polybutadiene resins derived from 1,3-butadiene monomer. These polybutadienes can be selected from 1,3-butadiene monomer.
• butadiene polymers are preferred to have a combination of cis- and trans- in- chain addition products from the extension of the polymerization through the
• polybutadiene (Elf Atochem). These polybutadienes typically contain pendant vinyl
• these polybutadienes can be modified by creating epoxy, ester, polyester, ether or polyether adducts, or by creating vinyl addition substituents such as styrene, polystyrene, acrylonitrile, acrylamide, acrylate, divinyl benzene, or other functions such as halogens, nitriles, etc.
• composition at a range from 30% to 95%>, preferably ranging from 50% to 70& by weight. They can be present in the Part B component in ranges from 25% to 97%, preferably ranging from 70% to 90%> by weight.
• Silanes Particularly the adhesion to silicon, metals and glass is desired.
• a silane coupling agent can be place in the Part A or Part B. It is preferred, however, to select silane coupling agents, having silyl ether groups capable of hydrolyzing to their respective silanols, and having isocyanato or oxirane functional
• Silanes compatible with the Part B reagent include bis(2-hydroxy ethyl)-3-aminopropyl
• Carbon blacks are typically necessary to provide a cosmetic function, often to
• reaction promoters serve to ensure complete formation of urethane or urea reactions. However, their level is maintained at a minimum effective level to ensure sufficient working time so
• reaction promoters such as organometallic or amine promoters for the reaction of active-hydrogen materials with isocyanates.
• amine promoters include tertiary amines such as triethylene diamine (Dabco, M&T Chemical).
• the group of organometallic promoters include organo-tin compounds such
• Witco UL-6 or dibutyltin dilaurate, or organomercury compounds such as phenyl

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• Computer Hardware Design (AREA)
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• Polyurethanes Or Polyureas (AREA)
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• 1999
  • 1999-01-26 EP EP99905475A patent/EP1084029A4/de not_active Withdrawn
  • 1999-01-26 WO PCT/US1999/001585 patent/WO1999038196A2/en not_active Application Discontinuation
  • 1999-01-26 JP JP2000528997A patent/JP2002502110A/ja active Pending

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