Leadframe Substrate with Crack Inhibiting Structure for Flip Chip Assembly
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Solution Overview
Problem
Current leadframe substrates face challenges in thermal management and mechanical reliability due to coefficient of thermal expansion (CTE) mismatch between heat dissipation elements and resin laminates, leading to potential cracking and electrical disconnection issues, especially in flip chip assemblies where routing circuitries span across interfacial boundaries.
Innovation Solution
A leadframe substrate is designed with a high thermal conductivity modulator having a low CTE, integrated with a resin layer and a crack inhibiting structure featuring a continuous interlocking fiber sheet that covers modulator/resin interfaces, preventing crack propagation and ensuring signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a heat dissipation element is bonded to the resin laminate, then thermal dissipation is improved, but cracking occurs due to CTE mismatch between the heat dissipation element and the resin laminate
Solution Approach 1:
The patent introduces an intermediary layer between the heat dissipation element and the resin laminate to act as a stress buffer. This intermediate structure absorbs the thermal expansion mismatch stresses, preventing direct stress transmission that causes cracking at the bonding interface, thereby maintaining both thermal dissipation performance and structural reliability.
Solution Approach 2:
The patent employs composite material structures combining different materials with complementary properties. The heat dissipation element is integrated with the resin laminate through a composite construction that leverages the high thermal conductivity of metal components and the low CTE of specific laminate materials, creating a unified structure that manages both heat flow and thermal stress.
2Reliability
If routing circuitries are disposed on the resin laminate portion, then electrical connection is achieved, but the circuitries must be spaced from the interfacial crack region to avoid electrical disconnection
Solution Approach 1:
The patent transitions routing circuitries from the two-dimensional resin laminate surface to the three-dimensional heat dissipation element surface. This dimensional shift allows routing paths to be established on the heat dissipation element where they are naturally spaced from the interfacial crack region between the heat dissipation element and resin laminate, eliminating the need to route around crack-prone areas while maintaining electrical connectivity.
3Reliability
If bonding wires are used to connect semiconductor chip to resin laminate, then electrical connection is achieved, but the wires must be spaced from the interfacial crack region
Solution Approach 1:
The heat dissipation element serves as an intermediary bonding substrate that replaces the resin laminate as the primary mounting surface for the semiconductor chip. By bonding the chip directly to the heat dissipation element, the bonding wires are positioned on a stable, crack-resistant surface that is thermally and mechanically integrated with the chip, eliminating the need to avoid interfacial crack regions and improving wire placement flexibility.
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 solution effectively addresses CTE mismatch-induced cracking, enhances thermal dissipation, and maintains signal integrity by using a low CTE modulator and a crack inhibiting structure to restrain cracks, thereby improving the reliability of flip chip assemblies.
Implementation Method 1
a high thermal conductivity modulator having a low CTE
Implementation Method 2
a crack inhibiting structure featuring a continuous interlocking fiber sheet that covers modulator/resin interfaces, preventing crack propagation
Data Source
AI summary
The leadframe substrate mainly includes a modulator, a plurality of metal leads, a resin layer and a crack inhibiting structure. The resin layer provides mechanical bonds between the modulator and the metal leads disposed about peripheral sidewalls of the modulator. The crack inhibiting structure includes a continuous interlocking fiber sheet that covers the modulator/resin interfaces, so that the segregation induced along the modulator/resin interfaces or cracks formed within the resin layer can be prevented or restrained from extending to the top surfaces, thereby ensuring the signal integrity of the flip chip assembly.