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Enhanced Electrical and Thermal Performance Wirebond Package Method Using Conductive Encapsulation

IP.com Disclosure Number: IPCOM000009748D
Original Publication Date: 2002-Sep-16
Included in the Prior Art Database: 2002-Sep-16
Document File: 3 page(s) / 89K

Publishing Venue

Motorola

Related People

Robert Wenzel: AUTHOR [+3]

Abstract

Current state of the art wirebond packages suffer from high inductance of the wirebond which severely limits electrical performance. Furthermore, signal wires and ground return wires are often distant from each other, creating a large loop inductance, high characteristic impedance and performance-robbing crosstalk for the signaling. Power and ground connections to the core of the die also suffer from high impedance and inductance that can significantly curtail the operational frequency of the device. Traditional encapsulations limit the thermal performance and drive products into much costlier alternative thermal-enhanced packages such as TBGA rather than PBGA.

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Enhanced Electrical and Thermal Performance Wirebond Package Method Using Conductive Encapsulation

Robert Wenzel

George Leal

David Wontor

Abstract

Current state of the art wirebond packages suffer from high inductance of the wirebond which severely limits electrical performance.� Furthermore, signal wires and ground return wires are often distant from each other, creating a large loop inductance, high characteristic impedance and performance-robbing crosstalk for the signaling.� Power and ground connections to the core of the die also suffer from high impedance and inductance that can significantly curtail the operational frequency of the device.� Traditional encapsulations limit the thermal performance and drive products into much costlier alternative thermal-enhanced packages such as TBGA rather than PBGA.

Convential wirebonding to rings or patches or costly flip-chip implementations are other ways to attempt to reduce inductance.� This idea is to use a conductive encapsulation of pre-insulated wirebonds and package top-side (or conformally-coated surfaces) rather than the conventional insulating mold compound.� Practical realization is achieved with appropriate dielectric coating applied to signal wires and non-contact areas.� A conductive encapsulation allows a coaxial signal path through the wire and provides a controlled impedance stripline for the substrate trace.� More ground connections to the die may be applied while avoiding the use of dedicated ground wires all together. These features provide many electrical and thermal benefits.

The benefit of the idea is that it significantly reduces or eliminates the electrical problems (such as high inductance and uncontrolled signaling impedance), creating a new state of the art in wirebond-based connection schemes.� In addition, electromagnetic interference can be greatly reduced by better containment of the electrical fields which is required for FCC compliance and qualification.� Fewer layers are required in the substrate since the ground plane is provided by the encapsulation, resulting in lower cost substrates.� The inductive electrical discontinuity of the wire is significantly reduced and made impedance-controlled to greatly increase the potential electrical performance of Radio-Frequency (RF) and Microwave devices as well as digital devices.� In addition, significant thermal conductivity is provided between the die and the top surface such that less expensive substrates may be used with still-air cooling schemes.         

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Discussion

The idea, shown in the diagram in Figure 1, can be applied to any or all wirebond-based packaging schemes.

Figure 1:� Electrically-enhanced and thermally-enhanced conductive-encapulation-based wirebond package.

The exposed ends of the insulated wire and other non-contact areas are insulated with a non-conducting epo...