Flexible Conductors for Stack Package Warpage Reduction
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Solution Overview
Problem
Conventional stack packages experience warpage and cracks due to mismatches in the coefficient of thermal expansion between component parts, such as epoxy molding compounds and copper posts, leading to reduced reliability.
Innovation Solution
The use of flexible conductors, like rolled-up or alternately curved flexible circuit boards with copper patterns, inserted into the encapsulation members to electrically connect stacked packages, reducing thermal expansion mismatches and stress between components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-solders or copper posts are used to achieve electrical connection between packages, then electrical connectivity is established, but warpage and cracks occur due to CTE mismatch between EMC and conductors
Solution Approach 1:
The patent changes the physical state and mechanical properties of the conductor material by using a flexible conductor with elastomeric characteristics instead of rigid pre-solders or copper posts. This parameter change in material rigidity allows the conductor to accommodate thermal expansion differences without causing warpage or cracks, thereby maintaining both electrical connectivity and structural stability during temperature cycling.
Solution Approach 2:
The patent employs a composite conductor structure consisting of a flexible circuit board substrate combined with conductive traces, where the flexible substrate acts as a stress-absorbing element. This composite material approach allows the conductor to maintain electrical functionality while accommodating dimensional changes due to CTE mismatch between different package components.
2Reliability
If rigid copper posts are used for electrical connection, then electrical conductivity is achieved, but cracks occur due to thermal expansion mismatch
Solution Approach 1:
The patent fundamentally changes the mechanical parameter of the conductor from rigid to flexible by using elastomeric materials. This parameter change enables the conductor to undergo elastic deformation during thermal cycling, absorbing the stress caused by CTE mismatch between EMC and conductors, thereby preventing crack formation while maintaining reliable electrical connection.
Solution Approach 2:
The flexible conductor acts as an intermediary element between the EMC and the electrical connection points. Its elastomeric properties allow it to mediate the thermal expansion forces, distributing and absorbing the stress that would otherwise concentrate at the interface between components with different CTE values, thus preventing crack propagation.
3Quantity of substance
If vertically stacked semiconductor packages are constructed, then data storage capacity is increased, but warpage occurs due to CTE mismatch between component parts
Solution Approach 1:
The patent changes the mechanical compliance parameter of the inter-package connector from rigid to flexible. This parameter change allows the vertically stacked packages to maintain proper alignment and shape during thermal cycling, as the flexible conductors can accommodate differential expansion between layers without causing warpage, thereby enabling high-density stacking while maintaining package integrity.
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
This configuration significantly reduces warpage by 50% and crack occurrence by 20-50% compared to conventional methods, enhancing the reliability of stack packages by mitigating thermal expansion-related issues.
Implementation Method 1
flexible conductors disposed in the first encapsulation member of the first package in such a way as to electrically connect the first package and the second package
Data Source
AI summary
A stack package includes a first package having a first semiconductor chip and a first encapsulation member which seals the first semiconductor chip. A second package is stacked on the first package, and includes a second semiconductor chip and a second encapsulation member which seals the second semiconductor chip. Flexible conductors are disposed within the first encapsulation member of the first package in such a way as to electrically connect the first package and the second package.