Coplanar Leveling Conductors for Non-Coplanar Package Substrate Pads
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Solution Overview
Problem
Non-coplanar configuration of metal pads on package substrates due to thermal expansion mismatch leads to unreliable solder joints, particularly in high-density thin film packages, where even slight surface irregularities significantly affect solder joint reliability.
Innovation Solution
A pad structure with first and second conductive pads and corresponding leveling conductors are formed on a package substrate, where the leveling surfaces of these conductors are made coplanar to ensure proper alignment and mounting of conductive contacts from a second package substrate, enhancing the reliability of electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal pads are fabricated on package substrate, then electrical connection is established, but non-coplanar top surfaces occur due to CTE mismatch causing solder joint failure
Solution Approach 1:
A leveling conductor is introduced as an intermediary layer between the non-coplanar metal pads and the solder joints. This leveling conductor has a bottom surface that contacts the non-coplanar pads and a top surface that provides a coplanar mounting surface for conductive contacts, thereby mediating the CTE mismatch issue and ensuring reliable electrical connections
2Productivity
If high density thin film circuitry is used with small pitch metal pads, then packaging density is improved, but surface irregularities significantly affect solder joint reliability
Solution Approach 1:
The leveling conductor serves as a mediator that decouples the high-density pad layout from the solder joint formation. By providing a coplanar top surface, it enables reliable solder joints even when the underlying pads are densely packed with small pitches, thus maintaining both high packaging density and solder joint reliability
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 coplanar leveling surfaces improve the reliability of electrical connections by ensuring accurate alignment and mounting of conductive contacts, thereby enhancing the stability and performance of solder joints in high-density thin film packages.
Implementation Method 1
Such non-coplanar configuration for the metal pads may occur mainly caused by fabrication process due to coefficient of thermal expansions (CTE) mismatch among materials being processed
Data Source
AI summary
A pad structure adapted to be disposed on a first package substrate and electrically connected to conductive contacts of a second package substrate includes a first conductive pad having a first top surface, a second conductive pad, a first leveling conductor and a second leveling conductor. The second conductive pad disposed aside the first conductive pad has a second top surface non-coplanar with the first top surface. The first leveling conductor disposed on the first conductive pad has a first leveling surface opposite to the first top surface. The second leveling conductor disposed on the second conductive pad and having a second leveling surface opposite to the second top surface is coplanar with the first leveling surface. The conductive contacts of the second package substrate are disposed on the first leveling conductor and the second leveling conductor. A manufacturing method of a pad structure is also provided.