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US20060163707A1 - Method and apparatus for reducing stresses applied to bonded interconnects between substrates - Google Patents

Method and apparatus for reducing stresses applied to bonded interconnects between substrates Download PDF

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Publication number
US20060163707A1
US20060163707A1 US11/039,975 US3997505A US2006163707A1 US 20060163707 A1 US20060163707 A1 US 20060163707A1 US 3997505 A US3997505 A US 3997505A US 2006163707 A1 US2006163707 A1 US 2006163707A1
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Prior art keywords
compound
substrate
pcb
scr
coupled
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US11/039,975
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Kean Hooi
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Google Technology Holdings LLC
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Motorola Inc
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Priority to US11/039,975 priority Critical patent/US20060163707A1/en
Assigned to MOTOROLA, INC. reassignment MOTOROLA, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HOOI, KEAN SEONG
Publication of US20060163707A1 publication Critical patent/US20060163707A1/en
Priority to US11/749,981 priority patent/US7642136B2/en
Assigned to Google Technology Holdings LLC reassignment Google Technology Holdings LLC ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: MOTOROLA MOBILITY LLC
Abandoned legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/552—Protection against radiation, e.g. light or electromagnetic waves
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/16—Fillings or auxiliary members in containers or encapsulations, e.g. centering rings
    • 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
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/301—Assembling printed circuits with electric components, e.g. with resistor by means of a mounting structure
    • 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
    • H01L2224/02—Bonding areas; Manufacturing methods related thereto
    • H01L2224/04—Structure, shape, material or disposition of the bonding areas prior to the connecting process
    • H01L2224/05—Structure, shape, material or disposition of the bonding areas prior to the connecting process of an individual bonding area
    • H01L2224/0554—External layer
    • 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
    • H01L2224/02—Bonding areas; Manufacturing methods related thereto
    • H01L2224/04—Structure, shape, material or disposition of the bonding areas prior to the connecting process
    • H01L2224/05—Structure, shape, material or disposition of the bonding areas prior to the connecting process of an individual bonding area
    • H01L2224/0554—External layer
    • H01L2224/0556—Disposition
    • H01L2224/05568—Disposition the whole external layer protruding from the surface
    • 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
    • H01L2224/02—Bonding areas; Manufacturing methods related thereto
    • H01L2224/04—Structure, shape, material or disposition of the bonding areas prior to the connecting process
    • H01L2224/05—Structure, shape, material or disposition of the bonding areas prior to the connecting process of an individual bonding area
    • H01L2224/0554—External layer
    • H01L2224/05573—Single external layer
    • 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
    • H01L2224/10—Bump connectors; Manufacturing methods related thereto
    • H01L2224/15—Structure, shape, material or disposition of the bump connectors after the connecting process
    • H01L2224/16—Structure, shape, material or disposition of the bump connectors after the connecting process of an individual bump connector
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/562—Protection against mechanical damage
    • 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
    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/00014—Technical content checked by a classifier the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
    • 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
    • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
    • H01L2924/161—Cap
    • H01L2924/1615—Shape
    • H01L2924/16152—Cap comprising a cavity for hosting the device, e.g. U-shaped cap
    • 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
    • H01L2924/30—Technical effects
    • H01L2924/301—Electrical effects
    • H01L2924/3025—Electromagnetic shielding
    • 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
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/10—Details of components or other objects attached to or integrated in a printed circuit board
    • H05K2201/10227—Other objects, e.g. metallic pieces
    • H05K2201/10371—Shields or metal cases
    • 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
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/10—Details of components or other objects attached to or integrated in a printed circuit board
    • H05K2201/10227—Other objects, e.g. metallic pieces
    • H05K2201/10393—Clamping a component by an element or a set of elements
    • 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
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/10—Details of components or other objects attached to or integrated in a printed circuit board
    • H05K2201/10613—Details of electrical connections of non-printed components, e.g. special leads
    • H05K2201/10621—Components characterised by their electrical contacts
    • H05K2201/10734—Ball grid array [BGA]; Bump grid array
    • 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
    • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/11—Treatments characterised by their effect, e.g. heating, cooling, roughening
    • H05K2203/1105—Heating or thermal processing not related to soldering, firing, curing or laminating, e.g. for shaping the substrate or during finish plating

Definitions

  • This invention relates generally to surface mount technology, and more particularly to a method and apparatus for reducing stresses applied to bonded interconnects between substrates.
  • an IC Integrated Circuit
  • BGA Bit Grid Array
  • PCB Printed Circuit Board
  • interconnect fractures when stresses from, for example, a mechanical drop are applied thereto.
  • liquid epoxy can be applied as underfill to fill gaps between the solder bumps of the BGA and the PCB as shown in FIG. 1 .
  • Embodiments in accordance with the invention provide a method and apparatus for reducing stresses applied to bonded interconnects between substrates.
  • a method for reducing stresses applied to one or more bonded interconnects of a substrate and a PCB (Printed Circuit Board).
  • the method comprises the steps of coupling a compound on a top surface of the substrate, wherein the compound has a property of expanding when a heat profile is applied thereto, coupling a cover to the PCB that overhangs at least a portion of the compound, and applying the heat profile to at least a portion of the foregoing components.
  • the heat profile can be applied to the compound and optionally to the cover and/or PCB.
  • a substrate for coupling to a PCB having one or more bonding interconnects is coupled to a bottom surface of the substrate for electrical bonding to the PCB, and a cover that overhangs at least a portion of a compound.
  • the compound has a property of expanding when a heat profile is applied thereto.
  • a process is applied to the foregoing components that couples the compound on a top surface of the substrate and to the cover when the heat profile is applied to at least a portion of the foregoing components.
  • a selective call radio having an optional display for presenting text and graphics to an end user of the SCR and an optional keypad for manipulating functions of the SCR includes a transceiver for processing signals from a communication system, a memory for storage, a power supply for supplying power to the components of the SCR, an audio system for presenting audible signals to the end user of the SCR, and a processor coupled to the foregoing components for control thereof.
  • One or more foregoing components of the SCR have a surface mount IC that couples to a PCB having one or more solder bumps, a compound having a property of expanding when a heat profile is applied thereto, a cover, and a double-sided adhesive.
  • a process can be applied to the foregoing components of the surface mount IC and the PCB that includes coupling the one or more solder bumps between an electrical pad of a bottom surface of the surface mount IC and a corresponding electrical pad on the PCB, coupling the double-sided adhesive between a surface of the compound and a top surface of the surface mount IC, coupling the cover on the PCB so that it overhangs at least a portion of the compound, and applying the heat profile to at least a portion of the foregoing components.
  • FIG. 1 is a diagram of a prior art IC (Integrated Circuit) packaged as a BGA (Ball Grid Array) with epoxy underfill applied to interconnects between the IC and a PCB (Printed Circuit Board).
  • BGA Bit Grid Array
  • FIGS. 2 and 3 are diagrams depicting a substrate for coupling to a PCB in accordance with an embodiment of the present invention.
  • FIG. 4 is a flow chart depicting the process applied to the substrate and PCB of FIGS. 2 and 3 for reducing stresses applied thereto in accordance with an embodiment of the present invention.
  • FIG. 5 shows a block diagram of a selective call radio (SCR) having one or more components utilizing the process depicted in FIGS. 2-4 in accordance with an embodiment of the present invention.
  • SCR selective call radio
  • FIGS. 2 and 3 are diagrams depicting the before and after effects of a process 200 (shown in FIG. 4 ) applied to a substrate 103 for coupling to a PCB 104 in accordance with an embodiment of the present invention.
  • the substrate 103 has one or more bonding interconnects 106 coupled to a bottom surface 113 of the substrate 103 and the PCB 104 a portion of which carry electrical signals to the PCB 104 .
  • the substrate 103 can comprise a surface mount IC (Integrated Circuit), herein referred to as IC 103 , carrying one or more conventional transistors and/or other conventional electrical components that produce a known function (e.g., a microprocessor, a memory, or a transceiver, just to name a few).
  • IC Integrated Circuit
  • the one or more bonded interconnects 106 can comprise one or more solder bumps, herein referred to as solder bumps 106 .
  • the solder bumps 106 are coupled to an electrical pad 114 of the bottom surface 113 of the IC 103 a portion of which can be electrically coupled to the electrical components carried by the IC 103 .
  • the solder bumps 106 are further coupled to a corresponding electrical pad 112 on a top surface 111 of the PCB 104 , which can be aligned with the electrical pads 114 of the IC 103 .
  • the electrical pads 112 of the PCB 104 provide connectivity to other components (not shown) located on the PCB 104 utilizing conventional technology such as traces and vias distributed among interconnecting layers of the PCB 104 .
  • the process 200 begins with step 204 where a conventional compound 108 A having a property of expanding when a heat profile is applied thereto is coupled to a top surface 109 of the IC 103 .
  • a double-sided adhesive 110 can be applied in step 202 to the epoxy compound 108 A for coupling to the top surface 109 of the IC 103 .
  • the double-sided adhesive 110 can be applied in step 202 to the top surface 109 of the IC 103 for coupling with the epoxy compound 108 A.
  • the compound 108 A can comprise a conventional epoxy resin, referred hereinafter as an epoxy 108 A.
  • any method suitable to the present invention can be used to couple the epoxy 108 A to the IC 103 .
  • any conventional compound 108 A having the property of expanding with application of a heat profile can be used also.
  • a cover 102 is coupled to the PCB 104 that overhangs at least a portion of the epoxy 108 A.
  • the cover 102 can be a conventional shield (herein referred to as a shield 102 ) that is electrically coupled to the PCB 104 for reducing EMI (Electromagnetic Interference) radiated by the IC 103 , and for reducing EMI entering the shield 102 .
  • the shield 102 can be electrically coupled by way of solder 116 interconnecting the shield 102 to an electrical pad (not shown) of the PCB 104 .
  • the portion of the shield 102 overhanging the epoxy 108 A has rigidity sufficient to reduce stresses applied to the one or more electrical bonded interconnects 106 . Such stresses can come about from physical drops or other forces applied to a device carrying the components of FIGS. 2 and 3 .
  • the shield 102 has been coupled to the PCB 104 , there may be gaps or voids 108 C and 108 D above and below the epoxy 108 A, respectively, as shown in FIG. 2 .
  • the gaps 108 C- 108 D are removed in whole or in part by the expansion of the epoxy 108 B as shown in FIG. 3 .
  • the epoxy 108 B serves to reduce stresses applied to the bonding interconnects 106 of FIG. 3 , thereby substantially eliminating stress fractures that may cause intermittent electrical failure.
  • One method to apply the heat profile in step 208 is with the use of a conventional reflow oven.
  • the reflow oven gradually applies heat to the components of FIG. 2 until reaching a peak temperature followed by a gradual cooling off cycle.
  • Heating profiles are well known in the art and can be adjusted to suit the compound and materials used in the assembly of the IC 103 and PCB 104 in FIG. 2 . Accordingly, any heat profile suitable to the present invention can be used and is not necessarily limited to a reflow oven.
  • FIGS. 2-4 can be embodied in one or more components of a selective call radio (SCR) 300 , a block diagram of which is shown in FIG. 5 in accordance with an embodiment of the present invention.
  • SCR selective call radio
  • the SCR 300 comprises conventional electrical components such as a transceiver 304 for processing signals from a communication system (such as a cellular network), a display 306 for presenting text and graphics to an end user of the SCR 300 , a keypad 308 for manipulating functions of the SCR 300 by way of, for example, a UI (User Interface) presented by the display 308 , a memory 310 for storage of software and data, a power supply 312 for supplying power to the components of the SCR 300 , an audio system 314 for presenting audible signals to the end user of the SCR 300 , and a processor 316 coupled to the foregoing components 304 - 314 for control thereof.
  • a transceiver 304 for processing signals from a communication system (such as a cellular network), a display 306 for presenting text and graphics to an end user of the SCR 300 , a keypad 308 for manipulating functions of the SCR 300 by way of, for example, a UI (User
  • the aforementioned process and apparatus of the present invention can be performed robotically thereby eliminating manual labor and improving manufacturing throughput.
  • the compound 108 can be applied to the substrate 103 in a controlled manner thereby eliminating messy applications and improving field serviceability.

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  • Physics & Mathematics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Computer Hardware Design (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
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Abstract

A method (200) is provided for reducing stresses applied to one or more bonded interconnects (106) of a substrate (103) and a PCB (Printed Circuit Board) (104). The method comprises the steps of coupling (204) a compound (108) on a top surface of the substrate, wherein the compound has the property of expanding when a heat profile is applied thereto, coupling (206) a cover (102) to the PCB that overhangs at least a portion of the compound, and applying (208) the heat profile to the compound and optionally the cover and/or PCB. More than one apparatus implementing the method is also included.

Description

    FIELD OF THE INVENTION
  • This invention relates generally to surface mount technology, and more particularly to a method and apparatus for reducing stresses applied to bonded interconnects between substrates.
    • BACKGROUND OF THE INVENTION
  • Typically, an IC (Integrated Circuit) packaged as a BGA (Ball Grid Array) having a high density of electrical interconnects bonded to a second substrate such as a PCB (Printed Circuit Board) is susceptible to interconnect fractures when stresses from, for example, a mechanical drop are applied thereto. To reduce these fractures, liquid epoxy can be applied as underfill to fill gaps between the solder bumps of the BGA and the PCB as shown in FIG. 1.
  • This process, however, is undesirable due to the manual labor involved during application, impact on manufacturing throughput, and often inconsistent and messy applications of liquid epoxy, which impacts serviceability of the end product.
  • The embodiments of the invention presented below overcome this disadvantage in the prior art.
    • SUMMARY OF THE INVENTION
  • Embodiments in accordance with the invention provide a method and apparatus for reducing stresses applied to bonded interconnects between substrates.
  • In a first embodiment of the present invention, a method is provided for reducing stresses applied to one or more bonded interconnects of a substrate and a PCB (Printed Circuit Board). The method comprises the steps of coupling a compound on a top surface of the substrate, wherein the compound has a property of expanding when a heat profile is applied thereto, coupling a cover to the PCB that overhangs at least a portion of the compound, and applying the heat profile to at least a portion of the foregoing components. The heat profile can be applied to the compound and optionally to the cover and/or PCB.
  • In a second embodiment of the present invention, a substrate for coupling to a PCB having one or more bonding interconnects is coupled to a bottom surface of the substrate for electrical bonding to the PCB, and a cover that overhangs at least a portion of a compound. The compound has a property of expanding when a heat profile is applied thereto. A process is applied to the foregoing components that couples the compound on a top surface of the substrate and to the cover when the heat profile is applied to at least a portion of the foregoing components.
  • In a third embodiment of the present invention, a selective call radio (SCR) having an optional display for presenting text and graphics to an end user of the SCR and an optional keypad for manipulating functions of the SCR includes a transceiver for processing signals from a communication system, a memory for storage, a power supply for supplying power to the components of the SCR, an audio system for presenting audible signals to the end user of the SCR, and a processor coupled to the foregoing components for control thereof. One or more foregoing components of the SCR have a surface mount IC that couples to a PCB having one or more solder bumps, a compound having a property of expanding when a heat profile is applied thereto, a cover, and a double-sided adhesive. A process can be applied to the foregoing components of the surface mount IC and the PCB that includes coupling the one or more solder bumps between an electrical pad of a bottom surface of the surface mount IC and a corresponding electrical pad on the PCB, coupling the double-sided adhesive between a surface of the compound and a top surface of the surface mount IC, coupling the cover on the PCB so that it overhangs at least a portion of the compound, and applying the heat profile to at least a portion of the foregoing components.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is a diagram of a prior art IC (Integrated Circuit) packaged as a BGA (Ball Grid Array) with epoxy underfill applied to interconnects between the IC and a PCB (Printed Circuit Board).
  • FIGS. 2 and 3 are diagrams depicting a substrate for coupling to a PCB in accordance with an embodiment of the present invention.
  • FIG. 4 is a flow chart depicting the process applied to the substrate and PCB of FIGS. 2 and 3 for reducing stresses applied thereto in accordance with an embodiment of the present invention.
  • FIG. 5 shows a block diagram of a selective call radio (SCR) having one or more components utilizing the process depicted in FIGS. 2-4 in accordance with an embodiment of the present invention.
    • DETAILED DESCRIPTION
  • While the specification concludes with claims defining the features of embodiments of the invention that are regarded as novel, it is believed that the embodiments of the invention will be better understood from a consideration of the following description in conjunction with the figures, in which like reference numerals are carried forward.
  • FIGS. 2 and 3 are diagrams depicting the before and after effects of a process 200 (shown in FIG. 4) applied to a substrate 103 for coupling to a PCB 104 in accordance with an embodiment of the present invention. The substrate 103 has one or more bonding interconnects 106 coupled to a bottom surface 113 of the substrate 103 and the PCB 104 a portion of which carry electrical signals to the PCB 104. In the present illustrations, the substrate 103 can comprise a surface mount IC (Integrated Circuit), herein referred to as IC 103, carrying one or more conventional transistors and/or other conventional electrical components that produce a known function (e.g., a microprocessor, a memory, or a transceiver, just to name a few).
  • The one or more bonded interconnects 106 can comprise one or more solder bumps, herein referred to as solder bumps 106. The solder bumps 106 are coupled to an electrical pad 114 of the bottom surface 113 of the IC 103 a portion of which can be electrically coupled to the electrical components carried by the IC 103. The solder bumps 106 are further coupled to a corresponding electrical pad 112 on a top surface 111 of the PCB 104, which can be aligned with the electrical pads 114 of the IC 103. The electrical pads 112 of the PCB 104 provide connectivity to other components (not shown) located on the PCB 104 utilizing conventional technology such as traces and vias distributed among interconnecting layers of the PCB 104.
  • Referring to FIG. 4, in its simplest embodiment the process 200 begins with step 204 where a conventional compound 108A having a property of expanding when a heat profile is applied thereto is coupled to a top surface 109 of the IC 103. In a supplemental embodiment, a double-sided adhesive 110 can be applied in step 202 to the epoxy compound 108A for coupling to the top surface 109 of the IC 103. Alternatively, the double-sided adhesive 110 can be applied in step 202 to the top surface 109 of the IC 103 for coupling with the epoxy compound 108A. The compound 108A can comprise a conventional epoxy resin, referred hereinafter as an epoxy 108A.
  • It would be appreciated by one of ordinary skill in the art that any method suitable to the present invention can be used to couple the epoxy 108A to the IC 103. Moreover, any conventional compound 108A having the property of expanding with application of a heat profile can be used also.
  • In step 206 a cover 102 is coupled to the PCB 104 that overhangs at least a portion of the epoxy 108A. The cover 102 can be a conventional shield (herein referred to as a shield 102) that is electrically coupled to the PCB 104 for reducing EMI (Electromagnetic Interference) radiated by the IC 103, and for reducing EMI entering the shield 102. The shield 102 can be electrically coupled by way of solder 116 interconnecting the shield 102 to an electrical pad (not shown) of the PCB 104. The portion of the shield 102 overhanging the epoxy 108A has rigidity sufficient to reduce stresses applied to the one or more electrical bonded interconnects 106. Such stresses can come about from physical drops or other forces applied to a device carrying the components of FIGS. 2 and 3.
  • Once the shield 102 has been coupled to the PCB 104, there may be gaps or voids 108C and 108D above and below the epoxy 108A, respectively, as shown in FIG. 2. When a heat profile is applied in step 208 to the aforementioned components of FIG. 2 the gaps 108C-108D are removed in whole or in part by the expansion of the epoxy 108B as shown in FIG. 3. After the epoxy 108B hardens, the epoxy 108B serves to reduce stresses applied to the bonding interconnects 106 of FIG. 3, thereby substantially eliminating stress fractures that may cause intermittent electrical failure.
  • One method to apply the heat profile in step 208 is with the use of a conventional reflow oven. The reflow oven gradually applies heat to the components of FIG. 2 until reaching a peak temperature followed by a gradual cooling off cycle. Heating profiles are well known in the art and can be adjusted to suit the compound and materials used in the assembly of the IC 103 and PCB 104 in FIG. 2. Accordingly, any heat profile suitable to the present invention can be used and is not necessarily limited to a reflow oven.
  • The foregoing structure and processes of FIGS. 2-4 can be embodied in one or more components of a selective call radio (SCR) 300, a block diagram of which is shown in FIG. 5 in accordance with an embodiment of the present invention.
  • The SCR 300 comprises conventional electrical components such as a transceiver 304 for processing signals from a communication system (such as a cellular network), a display 306 for presenting text and graphics to an end user of the SCR 300, a keypad 308 for manipulating functions of the SCR 300 by way of, for example, a UI (User Interface) presented by the display 308, a memory 310 for storage of software and data, a power supply 312 for supplying power to the components of the SCR 300, an audio system 314 for presenting audible signals to the end user of the SCR 300, and a processor 316 coupled to the foregoing components 304-314 for control thereof. Any one of the foregoing components 304-316 in whole or in part can utilize an IC 103 that couples to the PCB 104 as described above.
  • The aforementioned process and apparatus of the present invention can be performed robotically thereby eliminating manual labor and improving manufacturing throughput. In addition, the compound 108 can be applied to the substrate 103 in a controlled manner thereby eliminating messy applications and improving field serviceability.
  • In light of the foregoing description, it should be evident that embodiments in the present invention could be realized in numerous configurations contemplated to be within the scope and spirit of the claims below. It should also be understood that the claims are intended to cover the structures described herein as performing the recited function and not only structural equivalents. For example, although a nail and a screw fastener may not be structural equivalents in that the nail has no spiral threading like the screw fastener, a nail and a screw fastener can be used for securing objects firmly together, thereby making the nail and screw fastener equivalent structures. Accordingly, equivalent structures that read on the description provided herein are intended to be included within the scope of the invention as defined in the following claims.

Claims (20)

1. A method for reducing stresses applied to one or more bonded interconnects of a substrate and a PCB (Printed Circuit Board), comprising the steps of:
coupling a compound on a top surface of the substrate, wherein the compound has a property of expanding when a heat profile is applied thereto;
coupling a cover on the PCB so that it overhangs at least a portion of the compound; and
applying the heat profile to at least the compound.
2. The method of claim 1, wherein the substrate comprises a surface mount IC (Integrated Circuit), and wherein the one or more electrically bonded interconnects comprise one or more solder bumps coupled between an electrical pad of the bottom surface of the surface mount IC and a corresponding electrical pad on a top surface of the PCB.
3. The method of claim 1, wherein the compound comprises an epoxy resin.
4. The method of claim 1, further comprising the step of applying a double-sided adhesive to the compound for coupling to the top surface of the substrate.
5. The method of claim 1, further comprising the step of applying a double-sided adhesive to the top surface of the substrate for coupling to the compound.
6. The method of claim 1, wherein the cover comprises a shield electrically coupled to the PCB for reducing EMI (Electromagnetic Interference) radiated by the substrate, and for reducing EMI entering the shield.
7. The method of claim 1, wherein the portion of the cover overhanging the compound has rigidity sufficient to reduce stresses applied to the one or more electrically bonded interconnects.
8. A substrate for coupling to a PCB in an assembly, comprising:
one or more bonding interconnects coupled to a bottom surface of the substrate and the PCB;
a compound having a property of expanding when a heat profile is applied thereto, wherein the compound couples on a top surface of the substrate;
a cover coupled to the PCB and arranged to overhang at least a portion of the compound and coupled to at least a portion of the compound when applying the heat profile to the compound.
9. The substrate of claim 8, wherein the substrate comprises a surface mount Integrated Circuit (IC), and wherein the one or more bonded interconnects comprise one or more solder bumps coupled between an electrical pad of the bottom surface of the surface mount IC and a corresponding electrical pad on a top surface of the PCB.
10. The substrate of claim 8, wherein the compound comprises an epoxy resin.
11. The substrate of claim 8, wherein the assembly further comprises a double-sided adhesive applied between the compound and the top surface of the substrate.
12. The substrate of claim 8, wherein the cover comprises a shield electrically coupled to the PCB for reducing EMI (Electromagnetic Interference) radiated by the substrate, and for reducing EMI entering the shield.
13. The substrate of claim 8, wherein the portion of the cover overhanging the compound has rigidity sufficient to reduce stresses applied to the one or more electrically bonded interconnects.
14. The substrate of claim 8, wherein a portion of the one or more bonding interconnects carry electrical signals to the PCB.
15. A selective call radio (SCR), comprising:
a transceiver for processing signals from a communication system;
a memory for storage;
a power supply for supplying power to the components of the SCR;
an audio system for presenting audible signals to the end user of the SCR; and
a processor coupled to the foregoing components for control thereof, wherein one or more of the foregoing components of the SCR have a surface mount IC that couples to a PCB, comprising:
one or more solder bumps coupled between an electrical pad of a bottom surface of the surface mount IC and a corresponding electrical pad on the PCB;
a compound having a property of expanding when a heat profile is applied thereto;
a cover coupled to the PCB and arranged to overhang at least a portion of the compound and coupled to at least a portion of the compound when applying the heat profile to the compound; and
a double-sided adhesive applied between a surface of the compound and a top surface of the surface mount IC.
16. The SCR of claim 15, wherein the SCR further comprises a display for presenting text and graphics to an end user of the SCR and a keypad for manipulating functions of the SCR;
17. The SCR of claim 16, wherein the compound comprises an epoxy resin.
18. The SCR of claim 16, wherein the cover comprises a shield electrically coupled to the PCB for reducing EMI (Electromagnetic Interference) radiated by the surface mount IC, and for reducing EMI entering the shield.
19. The SCR of claim 16, wherein the portion of the cover overhanging the compound has rigidity sufficient to reduce stresses applied to the one or more solder bumps.
20. The SCR of claim 16, wherein a portion of the one or more bonding interconnects carry electrical signals to the PCB.
US11/039,975 2005-01-21 2005-01-21 Method and apparatus for reducing stresses applied to bonded interconnects between substrates Abandoned US20060163707A1 (en)

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