# US 2014/0193658 A1 · Low void solder joint for multiple reflow applications > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0193658 A1 - Document ID: US20140193658A1 - Status: Published application - Kind: A1 - Application number: 14/157,352 - Filed: 2014-01-16 - Published: 2014-07-10 - Earliest claimed: 2012-05-30 - Assignees: Indium Corporation - Applicants: Indium Corporation - Inventors: Jordan Peter Ross; Amanda Hartnett; Robert Norman Jarrett - Web page: https://patentgrep.com/patent/US20140193658A1 ## CPC - H05K 13/0465: {by soldering (H05K13/0469 takes precedence)} - H10W 40/10: Arrangements for heating - H10W 40/258: {Metallic materials (H10W40/254, H10W40/257, H10W40/255, H10W40/251, H10W40/253 take precedence)} - H10W 76/60: Seals - H10W 95/00: Packaging processes not covered by the other groups of this subclass - H10W 72/01325: {in solid form} - H10W 72/01351: {Changing the shapes of die-attach connectors} - H10W 72/072: {of bump connectors} - H10W 72/07236: {Soldering or alloying} - H10W 72/073: {of die-attach connectors} - H10W 72/07304: {the auxiliary member being temporary, e.g. a sacrificial coating} - H10W 72/07327: {involving guiding structures, e.g. spacers or supporting members} - H10W 72/07334: {Using a reflow oven} - H10W 72/07336: {Soldering or alloying} - H10W 72/07341: {Controlling the bonding environment, e.g. atmosphere composition or temperature} - H10W 72/332: {Plan-view shape, i.e. in top view} - H10W 72/334: {Cross-sectional shape, i.e. in side view} - H10W 72/352: {comprising metals or metalloids, e.g. solders} - H10W 72/877: {Bump connectors and die-attach connectors} - H10W 72/952: {comprising metals or metalloids, e.g. PbSn, Ag or Cu} - H10W 74/15: on active surfaces of flip-chip devices, e.g. underfills - H10W 90/724: {between a chip and a stacked insulating package substrate, interposer or RDL} - H10W 90/734: {between a chip and a stacked insulating package substrate, interposer or RDL} - H10W 90/736: {between a chip and a stacked lead frame, conducting package substrate or heat sink} - Y10T 428/12222: Shaped configuration for melting [e.g., package, etc.] - H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS - H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10 - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract Methods and apparatus are provided for attaching a heat spreader to a die and includes disposing a solder thermal interface material between a first surface of a die and a first surface of a heat spreader without disposing a liquid flux between the die and the heat spreader to form an assembly, wherein at least one of the first surface of the die and a first surface of the heat spreader have disposed thereon a metallization structure comprising a transition layer and a sacrificial metallization layer, the sacrificial metallization layer disposed as an outer layer to the metallization structure adjacent the solder thermal interface material; and heating the assembly to melt the thermal interface and attach the die to the heat spreader. ## Claims ### Claim 1 A method for attaching a heat spreader to a die, comprising: disposing a solder thermal interface material between a first surface of a die and a first surface of a heat spreader without disposing a liquid flux between the die and the heat spreader to form an assembly, wherein at least one of the first surface of the die and a first surface of the heat spreader have disposed thereon a metallization structure comprising a transition layer and a sacrificial metallization layer, the sacrificial metallization layer disposed as an outer layer to the metallization structure adjacent the solder thermal interface material; and heating the assembly in the presence of an inert oxide reducing gas under a first temperature profile to melt the solder thermal interface material thereby attaching the die to the heat spreader to form a soldered assembly, wherein the sacrificial metallization layer comprises a first metal soluble in the solder thermal interface material to form a eutectic composition with the second metal in the solder thermal interface material and create a package capable of undergoing subsequent reflow processes at equal or elevated temperature profiles. ### Claim 2 (depends on 1) The method of claim 1, wherein the step of heating the assembly takes place in a reflow oven, and further comprising: purging the reflow oven with an inert gas prior to the step of heating the assembly; and introducing the oxide reducing gas into the purged reflow oven prior to the step of heating the assembly. ### Claim 3 (depends on 1) The method of claim 1, wherein a metallization structure is provided on both the first surface of a die and a first surface of a heat spreader. ### Claim 4 (depends on 1) The method of claim 1, wherein the solder thermal interface material comprises indium and during the heating step the first metal dissolves in the indium, forming a eutectic of lower melting point than the indium. ### Claim 5 (depends on 1) The method of claim 1, wherein the solder thermal interface material comprises indium and during the heating step the indium melts and the first metal dissolves in the melted indium, allowing the melted indium to contact the transition layer. ### Claim 6 (depends on 5) The method of claim 5, wherein the indium forms an intermetallic interface with the transition layer. ### Claim 7 (depends on 6) The method of claim 6, wherein the transition layer comprises a metal having low solubility in indium such that the intermetallic interface formed is a stable intermetallic interface. ### Claim 8 (depends on 1) The method of claim 1, wherein the solder thermal interface material comprises indium and the first metal comprises silver, and during the heating step the silver dissolves in the indium, forming a eutectic of lower melting point than the indium. ### Claim 9 (depends on 1) The method of claim 1, wherein the solder thermal interface material comprises indium, the first metal comprises silver, and the transition layer comprises nickel, and during the heating step the indium melts and the silver dissolves in the melted indium, allowing the melted indium to contact the nickel and forming an In—Ni intermetallic interface. ### Claim 10 (depends on 1) The method of claim 1, wherein the first metal comprises at least one of silver, tin, zinc and cadmium. ### Claim 11 (depends on 1) The method of claim 1, wherein the transition layer comprises at least one of nickel and cobalt. ### Claim 12 (depends on 1) The method of claim 1, wherein the die has a perimeter and the metallization structure extends beyond the perimeter of the die to provide a reservoir of adherent material for reflow operations. ### Claim 13 (depends on 1) The method of claim 1, wherein the inert oxide reducing gas comprises a mixture of an organic acid in an oxygen-free carrier gas. ### Claim 14 (depends on 13) The method of claim 13, wherein the organic acid comprises acetic, formic or other carboxylic forms. ### Claim 15 (depends on 1) The method of claim 1, further comprising subjecting the assembly to a plurality of subsequent reflow processes, the plurality of subsequent reflow processes having higher temperature profiles than the first temperature profile. ### Claim 16 (depends on 1) The method of claim 1, further comprising mounting the soldered assembly on a circuit board and reflow soldering the soldered assembly to the printed circuit board. ### Claim 17 (depends on 1) The method of claim 1, further comprising mounting the soldered assembly on a circuit board and reflow soldering the soldered assembly to the printed circuit board wherein the reflow soldering is performed using a higher temperature profile than the first temperature profile. ### Claim 18 (depends on 1) The method of claim 1, further comprising: attaching the spreader to the substrate using a lid seal cure process; and applying a force to the spreader during the curing process, and wherein the solder preform has a predetermined thickness to provide a desired bondline or standoff height that is substantially the same as a finished bondline after reflow. ### Claim 19 (depends on 18) The method of claim 18, wherein the force is applied using a weight or a clip. ### Claim 20 (depends on 18) The method of claim 18, wherein the lid seal cure process does not hermetically seal the solid volume of solder. ### Claim 21 (depends on 1) The method of claim 1, wherein the a metallization layer on the heat spreader lacks a sacrificial metal layer. ### Claim 22 (depends on 1) The method of claim 1, further comprising inserting a fixture between the heat spreader and the die to maintain a predetermined standoff height during the step of reflow soldering. ### Claim 23 (depends on 22) The method of claim 22, further comprising forcing the heat spreader towards the die during the step of reflow soldering. ### Claim 24 (depends on 1) The method of claim 1, wherein the solid volume of solder has a textured surface adjacent to the heat spreader or the die. ### Claim 25 (depends on 1) The method of claim 1, wherein the solder thermal interface material comprises a first textured surface adjacent to the heat spreader and a second textured surface adjacent to the die. ### Claim 26 (depends on 1) The method of claim 1, wherein the solder thermal interface material is one of a plurality of solder thermal interface materials arranged between the die and the heat spreader and spaced apart by at least one channel. ### Claim 27 (depends on 1) The method of claim 1, wherein the solder thermal interface material comprises a plurality of slits extending from the center of the volume toward the periphery of the volume, wherein the slits are configured to close during the reflow solder process without forming voids. ### Claim 28 (depends on 1) The method of claim 1, further comprising not cleaning the soldered assembly prior to a subsequent reflow application. ### Claim 29 (depends on 1) The method of claim 1, wherein the first temperature profile includes a temperature sufficient to decompose an oxide reducing gas. ### Claim 30 A solderable assembly, comprising a die having a solderable surface; a heat spreader having a solderable surface positioned such that the solderable surface of the heat spreader is facing the solderable surface of the die; and a solder thermal interface material disposed between the solderable surface of the die and the solderable surface of the heat spreader, wherein at least one of the solderable surface of the die and the solderable surface of the heat spreader comprises a metallization structure comprising a transition layer and a sacrificial metallization layer, the sacrificial metallization layer disposed as an outer layer to the metallization structure adjacent the solder thermal interface material; wherein the solderable assembly is configured to be heated in the presence of an inert oxide reducing gas under a first temperature profile to melt the solder thermal interface material thereby attaching the die to the heat spreader to form a soldered assembly, wherein the sacrificial metallization layer comprises a first metal soluble in the solder thermal interface material to form a eutectic composition with the second metal in the solder thermal interface material and create a package capable of undergoing subsequent reflow processes at equal or elevated temperature profiles. ### Claim 31 (depends on 30) The solderable assembly of claim 30, wherein a metallization structure is provided on both the first surface of a die and a first surface of a heat spreader. ### Claim 32 (depends on 30) The solderable assembly of claim 30, wherein the solder thermal interface material comprises indium and during the heating step the first metal dissolves in the indium, forming a eutectic of lower melting point than the indium. ### Claim 33 (depends on 30) The solderable assembly of claim 30, wherein the solder thermal interface material comprises indium and during the heating step the indium melts and the first metal dissolves in the melted indium, allowing the melted indium to contact the transition layer. ### Claim 34 (depends on 33) The solderable assembly of claim 33, wherein the indium forms an intermetallic interface with the transition layer. ### Claim 35 (depends on 34) The solderable assembly of claim 34, wherein the transition layer comprises a metal having low solubility in indium such that the intermetallic interface formed is a stable intermetallic interface. ### Claim 36 (depends on 30) The solderable assembly of claim 30, wherein the solder thermal interface material comprises indium and the first metal comprises silver, and during the heating step the silver dissolves in the indium, forming a eutectic of lower melting point than the indium. ### Claim 37 (depends on 30) The solderable assembly of claim 30, wherein the solder thermal interface material comprises indium, the first metal comprises silver, and the transition layer comprises nickel, and during the heating step the indium melts and the silver dissolves in the melted indium, allowing the melted indium to contact the nickel and forming an In—Ni intermetallic interface. ### Claim 38 (depends on 30) The solderable assembly of claim 30, wherein the first metal comprises at least one of silver, tin, zinc and cadmium. ### Claim 39 (depends on 30) The solderable assembly of claim 30, wherein the transition layer comprises at least one of nickel and cobalt. ### Claim 40 (depends on 30) The solderable assembly of claim 30, wherein the die has a perimeter and the metallization structure extends beyond the perimeter of the die to provide a reservoir of adherent material for reflow operations. ### Claim 41 (depends on 30) The solderable assembly of claim 30, wherein the inert oxide reducing gas comprises a mixture of an organic acid in an oxygen-free carrier gas. ### Claim 42 (depends on 41) The solderable assembly of claim 41, wherein the organic acid comprises acetic, formic or other carboxylic forms. ### Claim 43 A soldered die and heat spreader assembly made by a process comprising the steps of: disposing a solder thermal interface material between a first surface of a die and a first surface of a heat spreader without disposing a liquid flux between the die and the heat spreader to form an assembly, wherein at least one of the first surface of the die and a first surface of the heat spreader have disposed thereon a metallization structure comprising a transition layer and a sacrificial metallization layer, the sacrificial metallization layer disposed as an outer layer to the metallization structure adjacent the solder thermal interface material; and heating the assembly in the presence of an inert oxide reducing gas under a first temperature profile to melt the solder thermal interface material thereby attaching the die to the heat spreader to form a soldered assembly, wherein the sacrificial metallization layer comprises a first metal soluble in the solder thermal interface material to form a eutectic composition with the second metal in the solder thermal interface material and create a package capable of undergoing subsequent reflow processes at equal or elevated temperature profiles. ### Claim 44 (depends on 43) The soldered die and heat spreader assembly of claim 43, wherein the step of heating the assembly takes place in a reflow oven, and further comprising: purging the reflow oven with an inert gas prior to the step of heating the assembly; and introducing the oxide reducing gas into the purged reflow oven prior to the step of heating the assembly. ### Claim 45 (depends on 43) The soldered die and heat spreader assembly of claim 43, wherein the solder thermal interface material comprises indium and during the heating step the first metal dissolves in the indium, forming a eutectic of lower melting point than the indium. ### Claim 46 (depends on 43) The soldered die and heat spreader assembly of claim 43, wherein the solder thermal interface material comprises indium and during the heating step the indium melts and the first metal dissolves in the melted indium, allowing the melted indium to contact the transition layer. ### Claim 47 (depends on 46) The soldered die and heat spreader assembly of claim 46, wherein the indium forms an intermetallic interface with the transition layer and wherein the transition layer comprises a metal having low solubility in indium such that the intermetallic interface formed is a stable intermetallic interface. ### Claim 48 (depends on 43) The soldered die and heat spreader assembly of claim 43, wherein the solder thermal interface material comprises indium and the first metal comprises silver, and during the heating step the silver dissolves in the indium, forming a eutectic of lower melting point than the indium. ### Claim 49 (depends on 43) The soldered die and heat spreader assembly of claim 43, wherein the solder thermal interface material comprises indium, the first metal comprises silver, and the transition layer comprises nickel, and during the heating step the indium melts and the silver dissolves in the melted indium, allowing the melted indium to contact the nickel and forming an In—Ni intermetallic interface. ### Claim 50 (depends on 43) The soldered die and heat spreader assembly of claim 43, wherein the die has a perimeter and the metallization structure extends beyond the perimeter of the die to provide a reservoir of adherent material for reflow operations.