Abstract:
An electrical structure, and associated method of fabrication, for reducing thermally induced strain in a structure that couples a first conductive body of a first substrate to a second conductive body of a second substrate (e.g., a chip to a chip carrier; a chip carrier to a circuit card). The melting point of the first conductive body exceeds the melting point of the second conductive body. The second conductive body may include eutectic lead-tin alloy, while the first conductive body may include non-eutectic lead-tin alloy. A portion of the first conductive body is coated with, or volumetrically surrounded by, a material that is nonsolderable and nonconductive. The first and second conductive bodies are coupled mechanically and electrically by surface adhesion at an uncoated portion of the first conductive body, by application of a temperature that lies between the melting points of the first and second conductive bodies.
Abstract:
A method and structure for reducing chip carrier flexing during thermal cycling. A semiconductor chip is coupled to a stiff chip carrier (i.e., a chip carrier having an elastic modulus of at least about 3×105 psi), and there is no stiffener ring on a periphery of the chip carrier. Without the stiffener ring, the chip carrier is able to undergo natural flexing (in contrast with constrained flexing) in response to a temperature change that induces thermal strains due to a mismatch in coefficient of thermal expansion between the chip and the chip carrier. If the temperature at the chip carrier changes from room temperature to a temperature of about −40° C., a maximum thermally induced displacement of a surface of the chip carrier is at least about 25% less if the stiffener ring is absent than if the stiffener ring is present. Since a propensity for cracking of the stiff chip carrier increases as the thermally induced displacement increases, the present invention, which avoids use of the stiffener ring, improves a structural integrity of the chip carrier.
Abstract:
A method of forming a printed circuit board or circuit card is provided with a metal layer which serves as a power plane sandwiched between a pair of photoimageable dielectric layers. Photoformed metal filled vias and photoformed plated through holes are in the photopatternable material, and signal circuitry is on the surfaces of each of the dielectric materials and connected to the vias and plated through holes. A border may be around the board or card including a metal layer terminating in from the edge of one of the dielectric layers. A copper foil is provided with clearance holes. First and second layers of photoimageable curable dielectric material is disposed on opposite sides of the copper which are photoimageable material. The patterns are developed on the first and second layers of the photoimageable material to reveal the metal layer through vias. At the clearance holes in the copper, through holes are developed where holes were patterned in both dielectric layers. Thereafter, the surfaces of the photoimageable material, vias and through holes are metalized by copper plating. This is preferably done by protecting the remainder of the circuitry with photoresist and utilizing photolithographic techniques. The photoresist is thereafter removed, leaving a circuit board or card having metalization on both sides, vias extending from both sides to the copper layer in the center, plated through holes connecting the two outer circuitized copper layers.
Abstract:
A method for forming a plated microvia interconnect. An external dielectric layer (EDL) is mounted on a surface of the substrate and is in direct mechanical contact with a conductive element included in the surface. An opening formed in the EDL exposes the conductive element and creates a microvia in the EDL. A sidewall and bottom wall surface of the microvia is treated to promote copper adhesion to the sidewall and bottom wall surfaces. The sidewall and bottom wall surfaces are plated to form a layer of copper thereon. The layer of copper is in direct mechanical and electrical contact with the conductive element. A wet solder paste deposited on the layer of copper overfills a remaining portion of the microvia. The solder paste is reflowed to form a solder bump in and over the remaining portion of the microvia to form the plated microvia interconnect.
Abstract:
A method and structure for reducing chip carrier flexing during thermal cycling. A semiconductor chip is coupled to a stiff chip carrier (i.e., a chip carrier having an elastic modulus of at least about 3×105 psi), and there is no stiffener ring on a periphery of the chip carrier. Without the stiffener ring, the chip carrier is able to undergo natural flexing (in contrast with constrained flexing) in response to a temperature change that induces thermal strains due to a mismatch in coefficient of thermal expansion between the chip and the chip carrier. If the temperature at the chip carrier changes from room temperature to a temperature of about −40° C., a maximum thermally induced displacement of a surface of the chip carrier is at least about 25% less if the stiffener ring is absent than if the stiffener ring is present. Since a propensity for cracking of the stiff chip carrier increases as the thermally induced displacement increases, the present invention, which avoids use of the stiffener ring, improves a structural integrity of the chip carrier.
Abstract:
A surface metal balancing structure for a chip carrier, and an associated method of fabrication, to reduce or eliminate thermally induced chip carrier flexing. A substrate, such as a chip carrier made of organic dielectric material, is formed and includes: internal circuitization layers, a plated through hole, and outer layers comprised of an allylated polyphenylene ether. A stiffener ring for mechanically stabilizing the substrate is bonded to an outer portion, such as an outer perimeter portion, of the top surface of the substrate, in light of the soft and conformal organic material of the substrate. The top and bottom surfaces of the substrate have metal structures, such as copper pads and copper circuitization, wherein a surface area (A) multiplied by a coefficient of thermal expansion (C) is greater for the metal structure at the bottom surface than for the metal structure at the top surface. A metal pattern is adjacent to the top surface so as to make the product AC of metal structures at or near the top and bottom surfaces approximately equal. The metal pattern reduces or eliminates flexing of the substrate in an elevated temperature environment, such as during a reflow of solder that couples a semiconductor chip to the substrate.
Abstract:
A method of forming a printed circuit card with a metal power plane layer between two photoimageable dielectric layers is provided. Photoformed metal filled vias and plated through holes are in the photopatternable material, and signal circuitry is on the surfaces of each of the dielectric materials connected to the vias and plated through holes. A border may be around the card including a metal layer terminating in from the edge of one of the dielectric layers. Copper foil with clearance holes is provided. First and second layers of photoimageable curable dielectric material are on opposite sides of the copper. Patterns are developed on the first and second layers of the photoimageable material to reveal the metal layer through vias. Through holes are developed where holes were patterned in both dielectric layers. The surfaces of the photoimageable material, vias and through holes are metallized by copper plating, preferably using photoresist.
Abstract:
A method and structure to electrically couple a semiconductor device to a substrate that is divided into a plurality of segments. Alternatively, a semiconductor device may be divided into a plurality of segments and the plurality of segments are electrically coupled to a single substrate.
Abstract:
A method and structure to electrically and mechanically join a first a first electrically conductive pad on a first substrate to a second electrically conductive pad on a second substrate using a solder joint that includes a low-melt solder alloy composition. The second electrically conductive pad has a geometry that compels a gap size of a gap between the first substrate and the second substrate to exceed a distance between the first substrate and a surface of the second pad.