Leadless Semiconductor Package with Thinned High-Aspect-Ratio Leads
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Solution Overview
Problem
The reliability of leadless semiconductor packages, such as QFN packages, is compromised due to long bond wires that are prone to shorting during encapsulation and the need for high-aspect-ratio leads that are susceptible to flexion and misalignment, leading to potential short circuits and alignment issues.
Innovation Solution
The implementation of high-aspect-ratio leads that are coupled to a die paddle and supported throughout the manufacturing process, with the back side of the leadframe being etched after molding compound curing to isolate and thin the leads, ensuring they remain stationary during encapsulation, and the use of a dielectric to cover thinned portions while maintaining contact surfaces for the package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If leads are made thinner to prevent contact with circuit board pads, then short circuit risk is reduced, but leads cannot support contact pads at significant distances
Solution Approach 1:
The leads have non-uniform cross-sections with different thicknesses at different locations. The leads are thinned in specific regions between contact pads to prevent unwanted contact, while maintaining adequate thickness in other regions to provide mechanical support for contact pads at extended distances. This localized variation in thickness allows both short circuit prevention and sufficient load-bearing capability.
2Area of stationary object
If high-aspect-ratio leads are used to achieve high contact density, then package size is reduced, but leads become susceptible to flexion and misalignment during manufacturing
Solution Approach 1:
The leadframe is etched to thin the leads between contact pads before encapsulation, and positioning structures are prepared in advance. This preliminary action ensures that high-aspect-ratio leads are locked into their final positions before any flexion or misalignment can occur during subsequent manufacturing steps, maintaining both compact package size and manufacturing precision.
Solution Approach 2:
The physical parameters of the leads are changed through the etching process, which modifies the thickness and structural properties of the leads. This parameter change creates leads with optimized mechanical properties that maintain rigidity and positioning accuracy despite the high aspect ratio required for compact packaging.
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 prevents movement and potential short circuits during encapsulation, ensuring the leads remain rigid and correctly aligned, enhancing the reliability and contact integrity of the semiconductor package.
Implementation Method 1
molding compound is deposited over a face of the leadframe on which the die paddle and leads are positioned. After the molding compound is cured
Implementation Method 2
a back side of the leadframe is etched to isolate the die paddle and leads, and to thin a portion of each of the leads
Data Source
AI summary
A leadless semiconductor package includes a package body on a leadframe that includes a die paddle and a plurality of high-aspect-ratio leads, each coupled at a first end to a contact pad of the package, and at a second end to a semiconductor die mounted to the die paddle. During manufacture of the package, molding compound is deposited over a face of the leadframe on which the die paddle and leads are positioned. After the molding compound is cured, a back side of the leadframe is etched to isolate the die paddle and leads, and to thin a portion of each of the leads. Back surfaces of the leads remain exposed at a back face of the body. The thinned portions of the leads are covered with a dielectric. During manufacture of the leadframe, a parent substrate is etched to define the die paddle and a plurality of leads on one side of the substrate and a plurality of cavities on the opposite face.