Hughes Aircraft Company

Hughes Aircraft

William D Gray

Cheng P Wen

Wah S Wong

Wah-Sang Wong

A high power, flip-chip microwave monolithic integrated circuit (MMIC) assembly (30) has a high power microwave monolithic integrated circuit (MMIC) having a surface with an active area (72) in which heat is generated. The assembly also has a host substrate (34). A thermally conductive bump (51) formed over the surface of the MMIC has a first portion (51') in close proximity to and in thermal communication with the active area (72) of the MMIC and a second portion (51') which is in close proximity to and in thermal communication with the host substrate (34). The second portion (51') of the thermal bump (51) has a greater cross-sectional area than the first portion (51'). A multi-layer, multi-exposure method of manufacturing the improved thermal bump (51) includes several steps. A plating membrane (80) is formed on a surface of the MMIC (32). A first layer of negative photoresist is applied to the surface of the plating membrane (80), and is exposed with a first masked pattern of light. A second layer of negative photoresist is applied on top of the first layer of photoresist. The second layer of negative photoresist is exposed with a second masked pattern of light. Unexposed areas of the first and second layers of photoresist form a 'T' shape. The first and second layers of photoresist are developed with a photoresist developer, thereby leaving a 'T'-shaped via in the photoresist. An electrically and thermally conductive metal is plated onto the plating membrane and into the via to form a substantially 'T'-shaped bump (51), which is then attached to a host substrate. The resulting bump has greater cross-sectional area at the host substrate than at the MMIC (32).

Flip chip high power monolithic integrated circuit thermal bumps

Flip chip high power monolithic integrated circuit thermal bumps and

A process is provided for passivating surfaces (12') of III-V microwave monolithic integrated circuit (MMIC) flip chips (40). Essentially, two cured, patterned polyimide layers (10, 28) are applied, one on the chip surface supporting a gold-plated bridge (26) and passivating the surface and the other over the gold-plated bridge to passivate the bridge surface. Further, a silver-titanium composite layer (32) is deposited over a gold-plated bump-post (24), which is then covered by a silver-plated bump (38), in order to prevent scavenging of gold from the bump-post by a subsequent Pb-Sn reflow solder process used to mount the chip to a metallized ceramic substrate. The process of the invention facilitates a more compatible reflow solder silk-screening process with passivated III-V MMIC flip chips, resulting in a more uniform and consistent solder thickness and relieving a tight tolerance requirement on the plated silver bump height uniformity.

Polyimide passivation of GaAs microwave monolithic integrated circuit

A gallium arsenide Monolithic-Microwave-Integrated-Circuit (MMIC) flip chip or other microelectronic circuit structure (10) includes a plated gold bridge (28) which serves as metal interconnect crossover between sites (24,-26) on a substrate (12). A first inorganic dielectric passivation layer (16), preferably of silicon dioxide, is formed under and supports the bridge (28). A second inorganic dielectric passivation layer (30), also preferably of silicon dioxide, is formed over and encapsulates the bridge (28) and the chip surface. A titanium/gold/titanium membrane (22) is formed under the bridge (28) to enable adhesion of the bridge (28) to the first passivation layer (16) and form plating contacts for the bridge (28). A contact bump post (38) is formed in a bump hole or via (32) which extends through the first and second passivation layers (16,30) to a bump contact site (34) on the substrate (12). Another titanium/gold/titanium membrane (40) is formed on the bump post (38) and the wall of the bump via (32) to provide a plating contact for a bump (42) which is plated on the membrane (40) inside the bump via (32) where the bump post (38) is located.

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Redondo Beach, CA, United States of America

William D Gray