Stackable Microelectronic Packages With Rigid Conductive Posts
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Solution Overview
Problem
Microelectronic packages face challenges in accommodating differential thermal expansion and contraction between semiconductor chips and circuit boards, leading to stress on solder connections, and in reliable testing due to non-planarity of terminals and solder balls, which complicates the construction of test fixtures and reduces their reliability.
Innovation Solution
The use of substantially rigid conductive posts projecting from a substrate, with an encapsulant layer that includes recesses or openings to expose conductive posts for electrical connections, allowing for flexible alignment and insulation of posts to carry different electric potentials, and a method of forming these posts and encapsulant layers to facilitate reliable electrical connections and thermal expansion compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If terminals are fixed relative to the chip using solder, then electrical connection is achieved, but stress from differential thermal expansion and contraction damages the solder connections
Solution Approach 1:
The patent implements movable terminals that can dynamically adjust their position relative to the chip. The terminal structure includes a terminal body that can move along a guide structure, allowing the terminal to accommodate thermal expansion and contraction differences between the chip and substrate. This dynamic adjustment capability prevents stress accumulation in the solder connections while maintaining reliable electrical contact throughout thermal cycling.
Solution Approach 2:
The patent changes the positional parameter of the terminals relative to the chip. By allowing the terminals to move along the guide structure, the system adapts to thermal dimensional changes. The terminal position is no longer fixed but can vary within a controlled range, accommodating the differential thermal expansion between materials without compromising connection integrity.
2Reliability
If solder balls are used for connections, then electrical connectivity is established, but non-planarity of solder balls complicates test fixture construction and reduces reliability
Solution Approach 1:
The patent employs a guide structure that constrains terminal movement to maintain coplanarity. The guide structure includes reference surfaces and positioning features that ensure all terminals remain at the same height relative to the substrate surface. This equipotential arrangement simplifies test fixture design by providing a uniform interface, eliminating the need for complex compensation mechanisms for non-planarity.
Solution Approach 2:
The guide structure acts as an intermediary between the chip and the test fixture. It provides a standardized, planar interface that mediates the connection between the movable terminals and the test equipment. This intermediary structure absorbs the complexity of terminal movement while presenting a simple, reliable interface to external testing equipment.
3Reliability
If terminals are made movable to compensate for thermal expansion, then stress on solder connections is reduced, but manufacturing precision and alignment become more difficult
Solution Approach 1:
The guide structure is pre-formed on the substrate with precise positioning features before the chip is mounted. The guide structure includes pre-defined movement paths, reference surfaces, and alignment features that establish the terminal positions and movement constraints in advance. This preliminary preparation ensures that when terminals are assembled, they automatically achieve correct alignment and coplanarity without requiring complex post-assembly adjustments.
Solution Approach 2:
The guide structure provides localized precision constraints at specific positions while allowing controlled movement in other degrees of freedom. The reference surfaces and positioning features are precisely formed only where needed to establish terminal positions, while the terminal bodies maintain manufacturing simplicity. This selective application of precision requirements balances manufacturing ease with alignment accuracy.
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 solution enhances the reliability of microelectronic packages by reducing stress from thermal expansion and improving testing by ensuring consistent electrical connections, while also extending the life of test fixtures by minimizing solder accumulation and enhancing the reliability of the engagement between the device and the test fixture.
Implementation Method 1
Assemblies including packages can suffer from stresses imposed by differential thermal expansion and contraction of the device and the substrate
Implementation Method 2
substantially rigid conductive posts projecting above the first surface... At least some conductive posts are electrically insulated from one another and adapted to simultaneously carry different electric potentials
Implementation Method 3
An encapsulant overlies at least a portion of the microelectronic element and the surface of the substrate above which the conductive posts project
Data Source
Figure 1A
Figure 1B
Figure 1C~1E
AI summary
A microelectronic package has a microelectronic element 110 overlying or mounted to a first surface 102 of a substrate 100 and substantially rigid conductive posts 106 projecting above the first surface or projecting above a second surface 104 of the substrate remote therefrom. Conductive elements 108 exposed at a surface of the substrate opposite the surface above which the conductive posts project are electrically interconnected with the microelectronic element. An encapsulant 130 overlies at least a portion of the microelectronic element 110 and the surface 102 of the substrate 100 above which the conductive posts 106 project, the encapsulant having a recess 336 or one or more openings 136, 236 each permitting at least one electrical connection to be made to at least one conductive post. At least some conductive posts 106 are electrically insulated from one another and adapted to simultaneously carry different electric potentials. In particular embodiments, the openings 136, 140, 146, 236 in the encapsulant 130 at least partially expose conductive masses 144 joined to posts, fully expose top surfaces 126 of posts 106 and partially expose edge surfaces 138 of posts, or may only partially expose top surfaces 126 of posts.