Patent GB-2600623-A (GB)
Title: System and method for forming solder bumps
Inventor: ERIC PETER LEWANDOWSKI
IPC: H01L27/18
Filed: 2020-06-17
Abstract: A method for forming a solder bump (122) includes preparing a transfer mold (100) having a solder pillar (112) extending from a mold substrate (102) and through a first photoresist layer (104) and having a shape partially defined by a second photoresist layer (108) that is removed prior to transfer of the solder; providing a device substrate (114) having a wettable pad (120); placing the transfer mold (100) and the device substrate (114) into aligned contact such that the solder pillar (112) is in contact with the wettable pad (120); forming a metallic bond between the solder pillar (112) and the wettable pad (120), e.g. by a cold welding process or a reflow process; and removing the mold substrate (102) and the first photoresist layer (104). The mold substrate (102) and the transfer mold (100) may be flexible. The transfer mold may comprise at least one of: a wetting layer over the mold substrate (402), in which case a pillar (112) including aluminum may be deposited and reflowed; a seed layer over the mold substrate (402); and a non-wetting layer over the second photoresist layer (408). The device substrate (114, 502) may comprise a through hole (118, 504) and may be an interposer made of silicon, glass and/or organic substrate material. The method may further comprise attaching the interposer (114, 502) to a qubit semiconductor device (a superconducting chip) (300, 516), wherein the qubit semiconductor device (300, 516) comprises a Josephson junction (304, 518), and wherein the attaching of the interposer (114, 502) to the qubit semiconductor device (300, 516) includes aligning the hole (118, 504) through the interposer (114, 502) with the Josephson junction (304, 518) to provide a path for accessing the Josephson junction (304, 518), in particular to make adjustments to its design frequency. The solder pillar (122) may be one of a plurality of solder pillars that are formed around the hole (118) between the qubit semiconductor device (300) and the interposer (114) for providing an amount of thermal isolation of the Josephson junction (304), forming a circular wall (200A, 200B) around the qubits and between the interposer (114) and the superconducting chip (300), wherein the circular wall (200A, 200B) may include at least one gap (202) therethrough. The solder pillar (512) may be one of a plurality of solder pillars (512) of the transfer mold, including a first solder pillar (512) having a first diameter and a second solder pillar (512) having a second diameter, the first diameter being larger than the second diameter. The device substrate (602) may comprise a semiconductor substrate comprising a deep recess (604), wherein a circuit component (608) may be comprised in the deep recess (604). The preparing of the transfer mold (100) may comprise: patterning the first and second photoresist layers (104, 108) to define a recess (110) that extends through the first and second photoresist layers (104, 108); and using injection molded soldering (IMS) to fill the recess (110) with solder to form the solder pillar (112). Alternatively, the preparing of the transfer mold may comprise: patterning the first and second photoresist layers (404, 408) to define a recess (410) that extends through the first and second photoresist layers (404, 408); forming a seed layer, wherein at least a portion of the seed layer is provided in the recess (410); and using electroplating to fill the recess (410) with solder and form the solder pillar. The pillars (112) may also be 3-D metal posts formed by copper plating or copper stud bumps.