Leadframe-Free QFN Package Structure for Oxidation-Resistant Soldering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional semiconductor packaging methods using leadframes limit the ability to construct compact structures due to routing density constraints and result in exposed leadframe ends, which are prone to oxidation, making sidewall solder wetting difficult.
Innovation Solution
A method for creating quad flat no-lead (QFN), dual flat no-lead (DFN), or small-outline no-lead (SON) packages without a leadframe, involving the use of conductive stumps, encapsulant layers, and a solderable metal system (SMS) or organic solderability preservative (OSP) to form conductive pads, eliminating exposed copper and burrs, and allowing for inset conductive pads within the package edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional leadframe packaging is used, then structural support is provided, but exposed leadframe ends are prone to oxidation and routing density is limited
Solution Approach 1:
The patent removes the leadframe entirely from the packaging structure, extracting the problematic component that causes oxidation and routing limitations. The leadframe is replaced with a substrate and encapsulant-based structure that eliminates exposed metal edges while providing necessary structural support and electrical interconnects.
Solution Approach 2:
The patent employs composite packaging structures combining substrate materials, encapsulants, and embedded conductive elements. This composite approach replaces the single-material leadframe with a multi-material system that achieves both structural integrity and oxidation resistance while enabling higher routing density through layered construction.
2Manufacturing precision
If capture pads are used to correct manufacturing inconsistencies, then connectivity is improved, but the ability to construct compact structures is limited
Solution Approach 1:
The patent incorporates alignment features and tolerance compensation directly into the substrate and encapsulant structure before final assembly. This preliminary action built into the packaging structure itself eliminates the need for additional capture pads, achieving manufacturing consistency without increasing package footprint.
3Ease of operation
If exposed copper is present on package periphery, then electrical connectivity is achieved, but solderability is difficult due to oxidation
Solution Approach 1:
The patent eliminates exposed copper from the package periphery by using encapsulant material to cover and protect all copper interconnects. Electrical connectivity is maintained through embedded conductive paths within the encapsulant or substrate, removing the oxidation-prone exposed metal surfaces that hinder solderability.
Solution Approach 2:
The encapsulant serves as an intermediary protective layer between the copper interconnects and the external environment. This mediator prevents direct exposure of copper to oxygen while maintaining electrical functionality, thereby preventing oxidation and improving solderability without compromising connectivity.
4Ease of manufacture
If conventional packaging methods are used, then structural support is provided, but burr formation occurs requiring additional processing steps
Solution Approach 1:
The patent removes the source of burr formation by eliminating the leadframe cutting process. Without leadframes requiring peripheral cutting, the problematic burr generation is eliminated entirely, reducing the number of additional processing steps needed for burr removal and improving manufacturing efficiency.
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 approach enables the formation of compact, oxidation-resistant packages with improved solderability and reduced burr formation, allowing for higher routing density and easier inspection of solder joints without the need for additional processing steps.
Implementation Method 1
forming a solderable metal system (SMS) or applying an organic solderability preservative (OSP) over the conductive pads to resist oxidation
Implementation Method 2
planarizing the encapsulant over an active layer of the semiconductor chip to create a planar surface
Implementation Method 3
forming a first conductive layer and first vertical conductive contacts over the planar surface and configured to be electrically coupled with the conductive stumps
Data Source
AI summary
A method and related structure for a quad flat no-lead (QFN), dual flat no-lead (DFN) or small outline no-lead (SON) package without a leadframe. Disposing semiconductor chips face-up on a temporary carrier, disposing a first encapsulant layer around the semiconductor chip, the active layer and conductive stumps, forming a conductive layer and conductive contacts over the planar surface, disposing encapsulant over the first encapsulant layer, conductive layer and conductive contacts, forming a photoresist over the encapsulant with openings, forming conductive pads within the openings, forming a solderable metal system (SMS) or applying an organic solderability preservative (OSP) over the conductive pads, and cutting through the encapsulant around the chip to form the outline of a package.