Flexible Printed Circuit Membrane for High-Density PIC Interconnects
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Solution Overview
Problem
Conventional methods for connecting photonic integrated circuits (PICs) to substrates, such as wire bonding and flip chip bonding, face challenges with high-density electrical connections, mechanical stress, and inefficient heat management due to the mechanical weakness of Indium Phosphide materials and the thermal path limitations of flip chip bumps.
Innovation Solution
A flexible printed circuit membrane (PCM) with a thin gold or copper conducting layer is used, providing high-density, low-stress electrical connections through thermosonic bonding and mechanical decoupling, allowing efficient heat management by direct attachment to heat sinks without additional thermal contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wire bonding is used to provide electrical connections, then electrical connections can be established, but wire length and density affect performance and manufacturability, and long wire bonds compromise high-speed performance
Solution Approach 1:
The invention extracts the wire bond from the system by replacing it with a flexible printed circuit membrane that provides direct electrical connections. This eliminates the need for long wire bonds that compromise high-speed performance while maintaining ease of manufacture through the membrane's integrated conductive traces.
Solution Approach 2:
The flexible printed circuit membrane acts as an intermediary between the substrate and external connections. It provides a compact, low-inductance path for electrical signals, replacing the long wire bonds with short, controlled-impedance traces that maintain high-speed performance.
2Quantity of substance
If flip chip bonding is used to provide high electrical contact density, then electrical connections can be established, but stresses from the bonding process and interconnect material can impair performance and reduce thermal performance
Solution Approach 1:
The invention uses a flexible printed circuit membrane with thin-film conductors to provide high electrical contact density. The flexible nature of the membrane allows it to conform to the substrate and provide numerous contact points without generating the mechanical stresses associated with rigid flip chip bonding, thereby maintaining both electrical and thermal performance.
Solution Approach 2:
The flexible printed circuit membrane employs composite material structures, combining flexible polyimide substrates with thin-film metal conductors. This composite approach enables high contact density while the flexible substrate absorbs mechanical stresses, preventing the performance impairment seen in traditional flip chip bonding.
3Temperature
If flip chip bonding is used to extract heat, then heat can be removed through bumps, but the small cross section of bumps provides a poor thermal path
Solution Approach 1:
The invention replaces the mechanical bump-based thermal path of flip chip bonding with a continuous thin-film conductor layer in the flexible printed circuit membrane. This thin-film path provides superior thermal conduction compared to discrete bumps, enabling efficient heat extraction while maintaining the electrical connection function.
4Reliability
If wire bonds are arranged between the interconnect substrate and electrically conducting terminal, then high-speed performance can be maintained, but bond wires provide a short thermal bridge that reduces TEC efficiency
Solution Approach 1:
The invention extracts the wire bonds from the thermal path between the interconnect substrate and electrically conducting terminals. By using the flexible printed circuit membrane's integrated traces instead of separate wire bonds, the thermal bridge effect is eliminated, allowing the thermoelectric cooler to operate at full efficiency while maintaining high-speed electrical performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The flexible PCM enables high-density, high-speed electrical connections with reduced mechanical stress and improved thermal performance, allowing efficient heat extraction and preventing damage to sensitive PIC features, while maintaining high-speed performance and maximizing surface area usage.
Implementation Method 1
A ball-shaped gold stud is arranged using thermosonic bonding for electrically connecting the at least one electrical contact and the conducting layer
Data Source
Figure 1~3a
Figure 3b~4
Figure 5~6
AI summary
An assembly (60) comprising a substrate (1) that is provided with at least one electrical contact (3a), a flexible printed circuit membrane (51) comprising an electrically insulating film (6) and an electrically conducting layer (7) that is at least partially covering the insulating film (6).The conducting layer (7) is at least locally accessible from outside of the membrane (51).A connection means (10) is further provided for electrically connecting the at least one electrical contact (3a) and the conducting layer (7) at a position where the conducting layer (7) is accessible, to form an electrical connection between the substrate (1) and the membrane (51). A chip package (70) comprising a housing (15) having at least one electrically conducting terminal, and an assembly (60) as mentioned. The flexible printed circuit membrane (51) is arranged for electrically connecting the substrate (1) and the at least one terminal of the housing (15).