No-Slump Solder Paste Vents for Warpage and Moisture in Semiconductor Packages
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Solution Overview
Problem
Current package-on-package (PoP) devices face challenges with warpage due to thermal effects and moisture outgassing, as through mold vias with solder bumps can lift off the substrate, and existing solutions require larger pitch and overdrilling, which are not effective in preventing warpage and moisture issues.
Innovation Solution
The use of a no-slump solder paste with a high-melting point metal, solder matrix, and polymer, which forms a conductive network through liquid phase sintering, volatilizes to create vents for moisture outgassing and provides mechanical continuity with an overmold layer having a high elastic modulus and thermal conductivity, matching the substrate's coefficient of thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If through mold vias with solder bumps are used to provide stand-off height, then adequate mechanical support is provided, but moisture outgassing is blocked causing pressure buildup and solder bump lifting
Solution Approach 1:
The patent employs a porous filler material within the through-mold via to maintain structural integrity while enabling moisture outgassing pathways. The porous structure allows moisture to escape during reflow processing without compromising the mechanical support function of the via, thereby preventing pressure buildup and solder bump lifting.
Solution Approach 2:
The invention uses a composite structure combining solder material with a porous filler material in the through-mold via. This composite approach allows the via to simultaneously provide mechanical support through the solder while enabling moisture outgassing through the porous filler, resolving the contradiction between structural strength and moisture venting capability.
2Object-generated harmful factors
If overdrilling is performed to prevent solder bump lifting, then moisture outgassing path is created, but larger pitch between interconnects is required
Solution Approach 1:
The porous filler material inherently provides moisture outgassing pathways within the via structure itself, eliminating the need for overdrilling operations. This allows maintenance of smaller pitch between interconnects while still enabling effective moisture venting during the reflow process.
3Strength
If thick mold layer is used to prevent warpage, then mechanical support is improved, but coefficient of thermal expansion mismatch and low elastic modulus cause susceptibility to warpage
Solution Approach 1:
The patent changes the material parameters of the mold layer by incorporating a porous filler material with appropriate thermal and mechanical properties. This modification adjusts the effective coefficient of thermal expansion and increases the elastic modulus of the mold layer, enabling warpage resistance without requiring excessive thickness.
Solution Approach 2:
The invention creates a composite mold layer structure combining the base mold material with porous filler material. This composite approach optimizes the thermal expansion characteristics and mechanical strength, providing superior warpage resistance compared to homogeneous mold materials of the same thickness.
4Ease of manufacture
If non-continuous mold layer is used with through mold vias, then via formation is simplified, but mechanical continuity is lost reducing warpage prevention effectiveness
Solution Approach 1:
The porous filler material is used to maintain mechanical continuity of the mold layer across the via regions. The porous structure allows the mold material to bridge over the via openings while maintaining structural integrity, thereby preserving mechanical continuity and warpage prevention capability without complicating the via formation process.
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 reduces warpage and allows for finer pitch interconnects without overdrilling, maintaining mechanical continuity and preventing moisture-related issues, while providing enhanced thermal conductivity and reduced z-heights in semiconductor packages.
Implementation Method 1
The interconnects are cured with a liquid phase sintering process to form a conductive network through the interconnects
Implementation Method 2
A polymer component of the no-slump solder paste may be volatilized after the curing process. The evacuated regions of the interconnects create a system of vents through which moisture may outgas
Implementation Method 3
an overmold over a die after the die has been bonded to the substrate... having a high elastic modulus and a CTE that is substantially similar to the substrate. The overmold layer may also have a high thermal conductivity
Data Source
AI summary
Embodiments describe a semiconductor package that includes a substrate, a die bonded to the substrate, and a solder paste overmold layer formed over a top surface of the die. In an embodiment, the solder paste comprises a high-melting point metal, a solder matrix, intermetallic compounds and a polymer. The overmold layer has a high elastic modulus, a coefficient of thermal expansion similar to the substrate, and reduces the warpage of the package. In an embodiment, interconnects of a semiconductor package are formed with a no-slump solder paste that includes vents. Vents may be formed through a conductive network formed by the high-melting point metal, solder matrix and intermetallic compounds. In an embodiment, vents provide a path through the interconnect that allows for moisture outgassing. In an embodiment, a mold layer may be mechanically anchored to the interconnects by the vents, thereby providing improved mechanical continuity to the mold layer.