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EP0551395A4 - Thermal stress-relieved composite microelectronic device - Google Patents

Thermal stress-relieved composite microelectronic device

Info

Publication number
EP0551395A4
EP0551395A4 EP19910918553 EP91918553A EP0551395A4 EP 0551395 A4 EP0551395 A4 EP 0551395A4 EP 19910918553 EP19910918553 EP 19910918553 EP 91918553 A EP91918553 A EP 91918553A EP 0551395 A4 EP0551395 A4 EP 0551395A4
Authority
EP
European Patent Office
Prior art keywords
substrate
reduced rigidity
region
component
volume
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19910918553
Other languages
French (fr)
Other versions
EP0551395A1 (en
Inventor
James C. Young
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
EIDP Inc
Original Assignee
EI Du Pont de Nemours and Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by EI Du Pont de Nemours and Co filed Critical EI Du Pont de Nemours and Co
Publication of EP0551395A1 publication Critical patent/EP0551395A1/en
Publication of EP0551395A4 publication Critical patent/EP0551395A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/12—Mountings, e.g. non-detachable insulating substrates
    • H01L23/14—Mountings, e.g. non-detachable insulating substrates characterised by the material or its electrical properties
    • H01L23/15—Ceramic or glass substrates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/12—Mountings, e.g. non-detachable insulating substrates
    • H01L23/13—Mountings, e.g. non-detachable insulating substrates characterised by the shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • 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
    • H01L2224/42—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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • 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
    • H01L2224/42—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
    • H01L2224/45147—Copper (Cu) as principal constituent
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • 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
    • H01L2224/42—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
    • H01L2224/4805—Shape
    • H01L2224/4809—Loop shape
    • H01L2224/48091—Arched
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • 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
    • H01L2224/42—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
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • 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
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/49—Structure, shape, material or disposition of the wire connectors after the connecting process of a plurality of wire connectors
    • H01L2224/491—Disposition
    • H01L2224/4912—Layout
    • H01L2224/49175—Parallel arrangements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • 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
    • H01L24/47—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
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • 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
    • H01L24/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L24/49—Structure, shape, material or disposition of the wire connectors after the connecting process of a plurality of wire connectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • 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
    • H01L2924/01014—Silicon [Si]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • 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
    • H01L2924/01079—Gold [Au]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/10—Details of semiconductor or other solid state devices to be connected
    • H01L2924/102—Material of the semiconductor or solid state bodies
    • H01L2924/1025—Semiconducting materials
    • H01L2924/10251—Elemental semiconductors, i.e. Group IV
    • H01L2924/10253—Silicon [Si]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/10—Details of semiconductor or other solid state devices to be connected
    • H01L2924/11—Device type
    • H01L2924/14—Integrated circuits
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/0201—Thermal arrangements, e.g. for cooling, heating or preventing overheating
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/0271—Arrangements for reducing stress or warp in rigid printed circuit boards, e.g. caused by loads, vibrations or differences in thermal expansion
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/03—Use of materials for the substrate
    • H05K1/05—Insulated conductive substrates, e.g. insulated metal substrate

Definitions

  • the invention relates to composite microelectronic devices which are configured to reduce the thermally induced stresses in the device generated by ordinary operation.
  • microelectronic devices such as VLSI (very large scale integration) silicon chips
  • VLSI very large scale integration
  • a typical composite package is comprised of a ceramic substrate on which is mounted firmly an integrated circuit (IC) chip.
  • the IC chip is electrically interconnected to a plurality of conductive and dielectric layers surrounding the chip which are also firmly attached to the substrate, but spatially separated from the chip.
  • Figures 1 and 2a show a typical composite package with a chip wire-bonded across a narrow channel to interconnected multiple conductive and dielectric layers surrounding the chip, and both the chip and the multilayer structure are attached firmly to a common base substrate.
  • This type of package involves several materials with different coefficients of thermal expansion and moduli of elasticity. A difference between operating temperatures and the temperature at which the package was manufactured results in thermally induced stresses and deformations that affect the reliability. They are very difficult to eliminate due to the inherent mismatch in the coefficients of thermal expansion between the multilayer component, usually made of copper and polyimide, and the silicon chip.
  • the conventional approach in this situation is to select a substrate material that produces the lowest stresses in both the chip and the multilayer component.
  • the present invention provides an improved substrate design that reduces the mechanical interaction among the three.
  • the invention is directed to a microelectronic device comprising a rigid substrate having a component mounted thereon, the component having a plurality of sides and an electrically functional layer adjacent to at least two sides of the component and the electrically functional layer being separated by a guard band, the volume of the substrate underlying the guard band having one or more regions of reduced rigidity which permit the substrate to flex, thereby to dissipate mechanical stresses generated therein when the device is subjected to heating.
  • guard band refers to the unoccupied surface area of a substrate which by virtue of physical spacing serves to isolate adjacent electrically functional elements mounted on the substrate.
  • Figure 1 is an orthographic projection of a conventional composite microelectronic package.
  • Figure 2a is a schematic section of a conventional composite microelectronic package and figures 2b through 2e are schematic sections of microelectronic packages which have been configured in accordance with the invention.
  • Figure 3a is a graphical representation of the in- plane normal stresses of a conventional microelectronic package and 3b is a graphical representation of such stresses in a like microelectronic package which has been configured in accordance with the invention.
  • Figure 4 is a bar chart which compares the in-plane thermal stresses of ungrooved and grooved substrates.
  • Figure 5 is a bar chart which compares the in-plane thermal stresses of copper layers on both ungrooved and grooved substrates.
  • Figure 6 is a bar chart which compares the in-plane thermal stresses of a silicon die mounted on both ungrooved and grooved substrates.
  • the patent is directed to a photoresist process for forming grooves in semiconductor materials for the purpose of isolation of integrated circuits.
  • the patent does not disclose or suggest the function of grooves in substrates for any reason.
  • the invention is based upon fabricating the substrate in such a manner that the attached chip expands and contracts at a rate relatively independently of the expansion and contraction rates of the remaining interconnected package components that are also attached to the substrate.
  • the substrate in accordance with the present invention includes a small flexible substrate region of reduced rigidity having a finite surface area wherein the area occupies a substantial space beneath the guard band that separates the chip and the surrounding package components.
  • This region of reduced rigidity is connected to two rigid substrate sections wherein one rigid section supports the chip and the other supports the remaining interconnected package components.
  • the flexible section provides a forgivable mechanical linkage between the two rigid sections wherein the chip attached to one rigid section can expand and contract more or less independently, irrespective of the expansion and contraction of other package components attached to the other rigid section.
  • the small flexible section can be a flexible material (Fig. 2b) or a thin section (Fig. 2c-e) formed by continuous or discontinuous grooves.
  • Fig. 2b the thermally-induced stress and deformation in the chip caused by other package components, or vice versus, are extremely small so that the changes for chip or interconnects failures are reduced.
  • the complete substrate or package has the traditional exterior dimensional appearance and overall is still very rigid structurally so that it can be handled with traditional package assembly methods. -.
  • Figures 1 and 2a illustrate the structure of a conventional composite microelectronic package consisting of an inert ceramic substrate 1 on which is firmly mounted an integrated circuit chip 3.
  • the substrate can be made of such materials as A1N, SiC, AI 2 O3, Si, quartz, mullite, cordierite and galium arsenide.
  • the chip 3 is adhered to substrate 1 by means of an adhesive layer 5 which may be either inorganic and/or organic in nature.
  • the adhesive layer also known as the die- attach layer, is an organic thermoplastic or thermoset polymer such as those which are disclosed in EP 88104940.7, which is incorporated herein by reference.
  • a dielectric layer 7 Surrounding the chip 3 is a dielectric layer 7 on which is mounted a series of conductive signal/power planes 9.
  • the chip and dielectric layer 7 are separated by a guard plane and the chip 3 is connected electrically to the signal/power planes 9 by a series of fine conductive wires 11 which are typically made of gold or copper metal.
  • the substrate 1 of Figure 1 has not been grooved or otherwise stress-relieved in accordance with the invention.
  • Figures 2b through 2e illustrate devices similar to that of Figures 1 and 2a, but differ in that each has a region of reduced rigidity to effect relief of the thermally induced stresses.
  • the reduced rigidity region is comprised of a solid material 13b which is a more flexible solid than the rigid material of the remainder of the substrate.
  • Figure 2c illustrates a package in accordance with the invention in which the region of reduced rigidity consists of a groove 13c cut into the top of the substrate and extending through about 80% of the substrate thickness.
  • the groove can be continuous around the outer edges of the chip or it can be intermittent or discontinuous so long as the degree of stress relief is sufficient.
  • Figure 2d illustrates a package in accordance with the invention in which the region of reduced rigidity is comprised of two grooves 13d - one extending into the substrate from the top of the substrate and the other from the bottom of the substrate.
  • Figure 2e then illustrates a similar package in which the region of reduced rigidity is a single groove 13e extending into the substrate from the bottom of the substrate.
  • the region or regions of reduced rigidity may extend continuously or discontinuously around the edges of the component so long as the region of reduced rigidity is sufficient to provide the desired degree of stress relief.
  • the ratio of the modulus of elasticity of the substrate containing a region of reduced rigidity to the modulus of elasticity of the remainder of the substrate (Modulus Ratio) be less than 0.3.
  • the grooves or other configuration which constitute the regions of reduced rigidity should not extend through more than 80% of the thickness of the substrate.
  • the term "rigid substrate” refers to substrates having a modulus of elasticity before modification in accordance with the invention of at least lOGpa.
  • the regions of reduced rigidity can be round-bottomed or square-bottomed, they can have vertical or sloped sides. In general, the sides of the grooves need not correspond with the edge of the guard level and the outer edge of the chip. Nevertheless, such configurations are preferred.
  • the over ⁇ riding consideration is whether the reduced rigidity regions are of sufficient volume to render the Modulus Ratio below 0.3 and preferably below 0.1. Compliance with this criterion of Modulus Ratio can readily be determined by direct measurement of the moduli or it can be determined by computer modeling and analysis of the system.
  • the substrate can be made simply of a single base material such as those mentioned above or it can be a composite material consisting of a dispersion of particles or fibers in a matrix of a base material or base material mixture. Fibers can be used as a substrate filler in order to increase substrate strength. On the other hand, heat-conductive materials may be added as well in order to increase the ability of the substrate to conduct heat away from the microelectronic component. In general, substrates will be on the order of 40-80 mils in thickness of which 60 mils is typical. Thermally induced stresses on the substrate tend to be directly related to thickness, whereas stresses in the surrounding dielectric layers tend to be inversely related to substrate thickness.
  • the regions of reduced rigidity, which are most frequently grooves be as close as possible to the chip but not underlying the chip.
  • the grooves surrounding a component will not exceed about 10 mils in width, which is the usual maximum width of the guard band in most composite packages.
  • the groove depth should not exceed about 80% of the substrate thickness. A substrate thickness of at least 10 mils should remain to avoid excessively weakening the mechanical strength of the substrate.
  • grooves When grooves are used to form the reduced rigidity region, they can be left open or they can be filled with a flexible material such as an elastomeric polymer or other non-rigid filler material.
  • Substrate (3.81x3.81x0.153cm) Laminant (2 planes with 1.53x1.53 cm cavity) Copper Layer (3.81x3.81x0.0036 cm) Dielectric Layer (3.81x3.81x0.0025 cm) Adhesive (3.81x3.81x0.0025 cm)
  • Groove dimensions are presented with the calculated maximum stresses shown in Table 1.
  • Table 1 data are presented showing the maximum in-plane thermal stresses incurred by the copper layer, the die attach adhesive and the die itself when they are heated to 170°C and allowed to cool to 20°C under ambient temperature conditions.
  • maximum stress data are given for these components on an ungrooved substrate and substrates having three groove configurations and several groove sizes. These data show that all three groove configurations - single groove up, single groove down and double grooves up - were effective to reduce residual in-plane thermal stresses in all three components. However, the double groove up configuration was most effective and the single groove up configuration was significantly more effective than the single groove down configuration.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Structure Of Printed Boards (AREA)
  • Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)

Abstract

A microelectronic package comprising a rigid substrate (1) having mounted thereon a component (3) having a plurality of sides and an electrically functional layer (9) adjacent to at least two sides of the component (3), the component (3) and the electrically functional layer (9) being spatially separated by a guard band (7), the volume of the substrate (1) underlying the guard band (7) having at least one region (13d) of reduced rigidity which permits the substrate (1) to dissipate mechanical stresses generated therein when the device is subjected to heating.

Description

THERMAL STRESS-RELIEVED COMPOSITE MICROELECTRONIC DEVICE
Field of Invention
The invention relates to composite microelectronic devices which are configured to reduce the thermally induced stresses in the device generated by ordinary operation.
Background of Invention
To accomplish high functional density, high speed and highly reliable operation, microelectronic devices, such as VLSI (very large scale integration) silicon chips, are increasingly being combined with an interconnected multilayer structure on a substrate to form a compact composite microelectronic package.
A typical composite package is comprised of a ceramic substrate on which is mounted firmly an integrated circuit (IC) chip. The IC chip is electrically interconnected to a plurality of conductive and dielectric layers surrounding the chip which are also firmly attached to the substrate, but spatially separated from the chip.
Figures 1 and 2a show a typical composite package with a chip wire-bonded across a narrow channel to interconnected multiple conductive and dielectric layers surrounding the chip, and both the chip and the multilayer structure are attached firmly to a common base substrate. This type of package involves several materials with different coefficients of thermal expansion and moduli of elasticity. A difference between operating temperatures and the temperature at which the package was manufactured results in thermally induced stresses and deformations that affect the reliability. They are very difficult to eliminate due to the inherent mismatch in the coefficients of thermal expansion between the multilayer component, usually made of copper and polyimide, and the silicon chip. The conventional approach in this situation is to select a substrate material that produces the lowest stresses in both the chip and the multilayer component. But a complex thermomechanical interaction still exists through the substrate, since it is impossible to match the coefficients of thermal expansion for the three key package components, i.e., the chip, the multilayer and the substrate, all at once. The present invention provides an improved substrate design that reduces the mechanical interaction among the three.
Summary of the Invention
The invention is directed to a microelectronic device comprising a rigid substrate having a component mounted thereon, the component having a plurality of sides and an electrically functional layer adjacent to at least two sides of the component and the electrically functional layer being separated by a guard band, the volume of the substrate underlying the guard band having one or more regions of reduced rigidity which permit the substrate to flex, thereby to dissipate mechanical stresses generated therein when the device is subjected to heating.
Definition:
As used herein, the term "guard band" refers to the unoccupied surface area of a substrate which by virtue of physical spacing serves to isolate adjacent electrically functional elements mounted on the substrate.
Brief Description of Drawings The drawing consists of six figures. Figure 1 is an orthographic projection of a conventional composite microelectronic package. Figure 2a is a schematic section of a conventional composite microelectronic package and figures 2b through 2e are schematic sections of microelectronic packages which have been configured in accordance with the invention. Figure 3a is a graphical representation of the in- plane normal stresses of a conventional microelectronic package and 3b is a graphical representation of such stresses in a like microelectronic package which has been configured in accordance with the invention. Figure 4 is a bar chart which compares the in-plane thermal stresses of ungrooved and grooved substrates. Figure 5 is a bar chart which compares the in-plane thermal stresses of copper layers on both ungrooved and grooved substrates. Figure 6 is a bar chart which compares the in-plane thermal stresses of a silicon die mounted on both ungrooved and grooved substrates.
Prior Art U,S, 3.325,882 and U.S. 3,428,86$, CtøPti ?t al
These divisional patents are directed to a packaging arrangement and method for interconnecting metal lands to a solid state device which is bonded to the floor of a cavity in the substrate so as to form a gap around the device to separate the device from the cavity walls. This is in contrast to the invention which uses a circumferential groove to decouple the stresses.
U,S. 4.374.457, tech gt al In this patent, iech provides a series of conductive filled grooves around the periphery of the cavity containing one or more semiconductor chips to form an electrical bus structure. In contrast with the invention multiple grooves are fabricated around the periphery of the cavity in the substrate and metallized.
U.S. 4.495.025 Haskell
The patent is directed to a photoresist process for forming grooves in semiconductor materials for the purpose of isolation of integrated circuits. The patent does not disclose or suggest the function of grooves in substrates for any reason.
Bar-Cohen "Bonding Relations for Natural Convection Heat Transfer from Vertical Printed Circuit Boards" - Proceedings of the IEEE, Vol. 73, No. 9, September 1985.
This article suggests that vertical and horizontal grooves that are machined in the surface of plates with component-carrying printed wiring boards enhance the heat transfer characteristics of the assembly when the plates are spaced closely together. However, there is no mention made of thermal-mechanical coupling effects and how these can be neutralized by grooving substrates around each component bonded to the substrate.
Petaifcd Descri tion of the Invention
The invention is based upon fabricating the substrate in such a manner that the attached chip expands and contracts at a rate relatively independently of the expansion and contraction rates of the remaining interconnected package components that are also attached to the substrate.
The substrate in accordance with the present invention includes a small flexible substrate region of reduced rigidity having a finite surface area wherein the area occupies a substantial space beneath the guard band that separates the chip and the surrounding package components. This region of reduced rigidity is connected to two rigid substrate sections wherein one rigid section supports the chip and the other supports the remaining interconnected package components. The flexible section provides a forgivable mechanical linkage between the two rigid sections wherein the chip attached to one rigid section can expand and contract more or less independently, irrespective of the expansion and contraction of other package components attached to the other rigid section.
As a feature of the present invention, the small flexible section can be a flexible material (Fig. 2b) or a thin section (Fig. 2c-e) formed by continuous or discontinuous grooves. In the complete package, the thermally-induced stress and deformation in the chip caused by other package components, or vice versus, are extremely small so that the changes for chip or interconnects failures are reduced. Yet the complete substrate or package has the traditional exterior dimensional appearance and overall is still very rigid structurally so that it can be handled with traditional package assembly methods. -.
Turning now to the Drawing, Figures 1 and 2a illustrate the structure of a conventional composite microelectronic package consisting of an inert ceramic substrate 1 on which is firmly mounted an integrated circuit chip 3. The substrate can be made of such materials as A1N, SiC, AI2O3, Si, quartz, mullite, cordierite and galium arsenide. The chip 3 is adhered to substrate 1 by means of an adhesive layer 5 which may be either inorganic and/or organic in nature. Typically, the adhesive layer, also known as the die- attach layer, is an organic thermoplastic or thermoset polymer such as those which are disclosed in EP 88104940.7, which is incorporated herein by reference. Surrounding the chip 3 is a dielectric layer 7 on which is mounted a series of conductive signal/power planes 9. The chip and dielectric layer 7 are separated by a guard plane and the chip 3 is connected electrically to the signal/power planes 9 by a series of fine conductive wires 11 which are typically made of gold or copper metal. The substrate 1 of Figure 1 has not been grooved or otherwise stress-relieved in accordance with the invention.
Figures 2b through 2e illustrate devices similar to that of Figures 1 and 2a, but differ in that each has a region of reduced rigidity to effect relief of the thermally induced stresses. In Figure 2b, the reduced rigidity region is comprised of a solid material 13b which is a more flexible solid than the rigid material of the remainder of the substrate. Figure 2c illustrates a package in accordance with the invention in which the region of reduced rigidity consists of a groove 13c cut into the top of the substrate and extending through about 80% of the substrate thickness. The groove can be continuous around the outer edges of the chip or it can be intermittent or discontinuous so long as the degree of stress relief is sufficient.
Figure 2d illustrates a package in accordance with the invention in which the region of reduced rigidity is comprised of two grooves 13d - one extending into the substrate from the top of the substrate and the other from the bottom of the substrate.
Figure 2e then illustrates a similar package in which the region of reduced rigidity is a single groove 13e extending into the substrate from the bottom of the substrate.
As mentioned above, the region or regions of reduced rigidity may extend continuously or discontinuously around the edges of the component so long as the region of reduced rigidity is sufficient to provide the desired degree of stress relief. In particular, it is preferred that the ratio of the modulus of elasticity of the substrate containing a region of reduced rigidity to the modulus of elasticity of the remainder of the substrate (Modulus Ratio) be less than 0.3. However, in order not to weaken the mechanical strength of the substrate excessively and make it too susceptible to breakage, the grooves or other configuration which constitute the regions of reduced rigidity should not extend through more than 80% of the thickness of the substrate. As used herein, the term "rigid substrate" refers to substrates having a modulus of elasticity before modification in accordance with the invention of at least lOGpa.
Various configurations can be used for the regions of reduced rigidity. For example they can be round-bottomed or square-bottomed, they can have vertical or sloped sides. In general, the sides of the grooves need not correspond with the edge of the guard level and the outer edge of the chip. Nevertheless, such configurations are preferred. The over¬ riding consideration is whether the reduced rigidity regions are of sufficient volume to render the Modulus Ratio below 0.3 and preferably below 0.1. Compliance with this criterion of Modulus Ratio can readily be determined by direct measurement of the moduli or it can be determined by computer modeling and analysis of the system. The substrate can be made simply of a single base material such as those mentioned above or it can be a composite material consisting of a dispersion of particles or fibers in a matrix of a base material or base material mixture. Fibers can be used as a substrate filler in order to increase substrate strength. On the other hand, heat-conductive materials may be added as well in order to increase the ability of the substrate to conduct heat away from the microelectronic component. In general, substrates will be on the order of 40-80 mils in thickness of which 60 mils is typical. Thermally induced stresses on the substrate tend to be directly related to thickness, whereas stresses in the surrounding dielectric layers tend to be inversely related to substrate thickness.
Because the microelectronic chip is the source of heat which gives rise to the thermally induced mechanical stresses, it is preferred that the regions of reduced rigidity, which are most frequently grooves, be as close as possible to the chip but not underlying the chip. Typically, the grooves surrounding a component will not exceed about 10 mils in width, which is the usual maximum width of the guard band in most composite packages. In addition the groove depth should not exceed about 80% of the substrate thickness. A substrate thickness of at least 10 mils should remain to avoid excessively weakening the mechanical strength of the substrate.
When grooves are used to form the reduced rigidity region, they can be left open or they can be filled with a flexible material such as an elastomeric polymer or other non-rigid filler material.
EXAMPLES
In Table 1 below, data are given which show the maximum in-plane thermal stresses which are incurred in cooling from 170°C to 20°C. A single chip composite package comprising a copper ground layer and an IC chip mounted by means of polymeric die attach adhesive to an aluminum substrate. Because of the technical difficulty in measuring actual in-plane stresses of such composite devices, the data were derived from finite element modeling of the deformation of each element based on the known TCE characteristics of each component. The dimensions of the components on which the modeling was based are as follows: IC chip (1.27x1.27x0.051 cm)
Substrate (3.81x3.81x0.153cm) Laminant (2 planes with 1.53x1.53 cm cavity) Copper Layer (3.81x3.81x0.0036 cm) Dielectric Layer (3.81x3.81x0.0025 cm) Adhesive (3.81x3.81x0.0025 cm)
Groove dimensions are presented with the calculated maximum stresses shown in Table 1. In Table 1, data are presented showing the maximum in-plane thermal stresses incurred by the copper layer, the die attach adhesive and the die itself when they are heated to 170°C and allowed to cool to 20°C under ambient temperature conditions. In particular, maximum stress data are given for these components on an ungrooved substrate and substrates having three groove configurations and several groove sizes. These data show that all three groove configurations - single groove up, single groove down and double grooves up - were effective to reduce residual in-plane thermal stresses in all three components. However, the double groove up configuration was most effective and the single groove up configuration was significantly more effective than the single groove down configuration.
Table 1 In-Plane Residual Stresses of Grooved and Ungrooved Substrates - Effect of Groove Size and Configuration
(1) Width/depth in mils The data given in the second column of the above Table with respect to thermal stresses in the copper layer can be observed graphically in Figure 4.

Claims

1. A microelectronic device comprising a rigid substrate having a component mounted thereon, the component having a plurality of sides and an electrically functional layer adjacent to at least two sides of the component, at least two sides of the component and the electrically functional layer being separated by a guard band, the volume of the substrate underlying the guard band having at least one region of reduced rigidity which permits the substrate to flex, thereby to dissipate mechanical stresses generated therein when the device is subjected to heating.
2. The device of claim 1 in which the region of reduced rigidity is continuous.
3. The device of claim 1 in which the ratio of the modulus of elasticity of the volume of the substrate containing a region of reduced rigidity to the modulus of elasticity of the remainder of the substrate (Modulus Ratio) is less than 0.3.
4. The device of claim 3 in which the Modulus Ratio is less than 0.1.
5. The device of claim 1 in which the substrate has a predetermined thickness and the region of reduced rigidity has a predetermined depth which does not exceed 80% of the substrate thickness.
6. The device of claim 1 in which the modulus of elasticity of the unmodified substrate is at least 10 Gpa.
7. The device of claim 1 in which the region of reduced rigidity has a predetermined width which corresponds with the width of the guard band. 8. The device of claim 7 in which the region of reduced rigidity extends from the upper surface into the volume of the substrate.
9. The device of claim 7 in which the region of reduced rigidity extends from the lower surface into the volume of the substrate.
10. The device of claim 1 having a plurality of reduced rigidity regions.
1 1. The device of claim 10 in which the regions of reduced rigidity extend from the upper surface into the volume of the substrate.
12. The device of claim 10 in which the regions of reduced rigidity alternately extend from the upper and lower surfaces into the volume of the substrate.
13. The device of claim 12 in which a first region of reduced rigidity extends from the upper surface into the volume of the substrate adjacent to the edge of the component.
14. The device of claim 1 in which the region of reduced rigidity is a groove.
15. The device of claim 14 in which the groove is continuous.
16. The device of claim 1 in which the region of reduced rigidity is comprised of a discontinuous series of grooves.
17. The device of claims 14 or 15 in which the grooves are filled with an inert non-rigid solid material. 18. The device of claim 1 in which the region of reduced rigidity is comprised of non-rigid material which is an integral part of the substrate.
19. The device of claim 1 in which the substrate is a composite layer of particles dispersed in a rigid solid matrix.
20. The device of claim 1 in which the substrate is a composite layer of fibers dispersed in a rigid solid matrix.
21. The device of claim 1 in which the substrate is comprised of ceramic solid material selected from A1N, SiC, AI2O3, silicon, quartz, mullite, cordierite and galium arsenide.
22. The device of claim 1 in which the substrate is comprised of rigid polymeric material.
23. The device of claim 1 in which the component is an integrated circuit chip.
24. The device of claim 1 in which the electrically functional layer is a dielectric layer.
25. The device of claim 1 in which the substrate has a plurality of components mounted thereon.
EP19910918553 1990-09-27 1991-09-18 Thermal stress-relieved composite microelectronic device Withdrawn EP0551395A4 (en)

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JPH06503207A (en) 1994-04-07
EP0551395A1 (en) 1993-07-21

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